Croatia Itinerary without Car?

I like your itinerary.

One other option is Flixbus. We took Zagreb - Zadar bus - 3 hrs, $12. Bus stopped for potty break at 2 hrs. Nice new bus, very pleasant. Flixbus has a lot of routes. Buses may stop in Nov but should run fine in September.

From Split to Zadar you do not need a transfer. Busses run from Split to Zadar about every hour, and the bus station is right where the ferry docks. Just buy a ticket, and get on the next bus. Most buses follow the coast, and it is a nice ride.

Pula to Rovinj can be a bit more complicated. We took a taxi then.

I would try to avoid renting a car in one country and dropping of in another. In order to get to Ljubliana you could consider the train. In summer there are direct trains Pula - Ljubljana, and you could get a taxi from Rovinj to one of the stations on that line, and continue by train.

This info is based on my trip in 2015, so verify current conditions:

• In addition to bus tours (I assume), there are public buses between Dubrovnik and Kotor, though they're not super-frequent. They could easily get swamped by folks arriving on cruise ships, so I wouldn't want to wait until the day of travel to buy the ticket. Frequency (and also demand) might vary by day of week, so check that before deciding when to do the day trip. Kotor is vastly more atmospheric when there's not a cruise ship in port, so that's something else to check before pinning down your date. Even if the town itself (or at least the part within the walls near the coast) is crowded, the scenery around the Bay of Kotor is stunning. It's a great idea to take a bus rather than renting a car, because I think the driver wouldn't get to fully enjoy the views.

• I don't know whether you'd have time (maybe if you hit a super-busy day in Kotor and don't spend a great deal of time in the town?), but I enjoyed stopping off in Herceg-Novi for a couple of hours or so. At least some of the buses between Dubrovnik and Kotor stop there, but check the location of the bus station vis-a-vis the old town to be sure you wouldn't have an impractically long walk.

• There are public buses between Rovinj and both Pula and Porec. I also enjoyed a shortish stop in the tiny, coastal, hilltop town of Vrsar.

• There are buses, perhaps just once a day, between Rovinj and Ljubljana; this I checked, and Flixbus now operates them. I'm glad to know rail service between Pula and Ljubljana is an option, but at the moment the bus seems to be a good bit faster.

• I've always purchased tickets for cross-border buses somewhat in advance. Service is usually limited, as here, and they can definitely sell out. With luck the bus website(s) will show the number of available tickets, so you can keep tabs on the situation. This applies to the Kotor day trip as well as the Ljubljana-Rovinj trip.

• I've never read that Flixbus does this, but the Croatian bus company/companies I used charged a modest fee for each piece of luggage placed in the hold. If a bus-company employee standing beside the hold sticks out his hand, that's what it's about; it's not a scam. The cost was the equivalent of about $1 in 2015 but could be higher now.

I enjoyed walking around the atmospheric historic center of Zadar. It wasn't totally devoid of tourists, but it was so much more peaceful than Dubrovnik is these days! Do allow yourselves some time there.

Zadar – We climbed the Bell Tower of the Zadar Cathedral shortly before sunset. What a beautiful view over the town and the sea.

Please consider that in September the ferry Zadar to Pula runs 3 days a week only.

Mali Losinj - How many beach activities are you planning? Or is it more about costal walks (or rent bicycle) and the atmosphere?
Don’t miss the small but nice Museum of Apoxyomenos https://www.muzejapoksiomena.hr/en/ and the fragrant garden https://miomirisni-vrt.hr/en/
The costal walk from Valdarke bay to Veli Losinj is beautiful and Čikat bay is the destination for swimming and marveling at old Habsburg villas that have since been restored into luxury hotels.

Arrival in Pula by ferry will be late evening. Maybe it would be easier to spend a night in Pula, use the morning to visit the Roman amphitheater and then move on by bus to Rovinj.

Pula to Rovinj is served by several bus companies. https://www.buscroatia.com/ helps to find the bus operators for one route. https://www.arriva.com.hr/en-us/home is the most common one in Istria. Rovinj to Ljubljana I would recommend Flixbus, alternatively bus to Rijeka and train to Ljubljana.

Thank you very much for all the amazing feedback and recommendations. Wow, you helped so much!! I also didn't realize the ferry was only 3 days a week in September so thank you! Based on that change, we are looking at possibly adding another night in Zadar. It seems like you all really like Zadar but please let me know if you think 2 nights is too long. We are also trying to see if we can fit in Mali Losinj or should go straight to Pula. Our favorite things are swimming, coast walks and we love going to dinner and having a few drinks watching the sunset. Do you think we can get all that in Rovinj or should we make sure to stay in Mali Losinj?

Thanks again for all the amazing help!

2 nights in Zadar might be a bit long. The city beach of Zadar (Kolovare Beach) is not that great. In that case, I would recommend taking a boat trip to the Kornati National Park.

All I know of Rovinj is the old town (and yes, it's wonderful) on the peninsula and the harbor. I can't say how easy it is to find a nice place to swim.

Here is the sailing schedule of the Zadar -Pula ferry:
https://krilo.hr/en/sailing-schedule/pula-unije-susak-mali_losinj-ilovik-silba-zadar/
Thus 2 nights in Mali Losinj would work Wednesday to Friday or Friday to Sunday.