Travel from Split to Dubrovik

Check out Dubrovnik Riviera Tours. We wish we had done what you propose instead of renting a car.

You could always take a bus or boat, which is how most people make this journey. It won’t take much longer than hiring a driver.

Agree with Jennifer--it's about four hours on the bus, perfectly comfortable. If you had no plans to stop, this would be my choice. I just can't see paying a premium for this journey.
For a more scenic route, check the catamaran schedule. Krilo and Jadrolinija are the operators.

If you don’t have some specific timeline or too much luggage or particular mobility concerns, I would do what Jennifer suggested. But then I love any excuse to get on the water. And it’s not expensive. There’s only one a day, using this line. https://www.krilo.hr/en/sailing-schedule/split-dubrovnik/. Then you could taxi to (or close to) your lodging.

Autoeurope.com will give you some choices on car rental in case you go that direction.

You can go by ferry, check krilo.hr for info and tickets. Whenever we rent a car in Croatia, we return it either in Split or Dubrovnik, whichever is our first stop. There is very limited parking in both cities and driving can be very stressful.

While we haven't hired a car and driver for the Split to Dubrovnik, we have hired drivers on more than one occasion in Croatia and have been very satisfied, both for domestic and cross-boarder travel. Having the driver negotiate and answer questions at the Bosnia-Herzogovina border saved me some anxiety. Someone mentioned the bus, which is good. For some fun, check out Krilo and Jadrolinija service, too. It was a very easy, scenic and fun trip from Split to Dubrovnik and it wasn't expensive.

I'd take the boat. Done that 2x now. Pleasant trip, snacks on boat available.

In 2017 we rented a car in Dubrovnik and drove to Split. Rather than cross a border, we did a short hop on a car ferry from Trpanj (on the Peljesac Peninula) to Ploce. I purchased the ferry tickets in advance on-line. The peninsula was interesting. More details on this drive are in my trip report posted in this forum at the following URL. https://community.ricksteves.com/travel-forum/trip-reports/croatia-road-trip-aug-2017-dubrovnik-and-drive-to-split

Thank you for all of the suggestions!

A couple of years ago, on my maiden trip to Croatia, I went from Dubrovnik to Split (reverse commute than your's but still relevant) via public transport (https://getbybus.com/en/bus-split-to-plitvice-lakes) making a 6 hr stop at Plitvice national park (https://np-plitvicka-jezera.hr/). I would highly recommend it .. the bus runs regularly and is extremely comfortable and has enough space for your luggage. Note: you'll need to purchase 2 separate tickets, Split->Plitvice and Plitvice->Dubrovnik. There are luggage rooms at the entrance of Plitvice park and I stored my luggage there for 5/6 hours as I explored the park. It is a beautiful park - I loved hiking, walking, and also took the boat tour in the park. At the entrance, they provide with trail maps and the times it'll take you to explore/hike. So, pick the trails accordingly. You can explore the park in 4/5 hours easily. And then continue the bus ride to Dubrovnik.
Hope it helps.

Just got back from Croatia--easy trip!! Due to covid concerns we used mydaytrip.com (based on a R.S. team recommendation) to get a private car--vaccinated, face masks, and personal. Felt very safe! And impromtu tour guide as well. The border crossing through Bosnia Herzegovna is absolutely no problem.