In June, I will be going to Mostar from Dubrovnik for 1 night, then stopping by Blagaj and Pocitelj before going to Split. I have not been able to find any stand alone GPS or iPhone offline GPS app with voice turn-by turn with good Bosnia-Herzegovina map. How did you navigate driving? I will be buying a SIM card in Croatia so that I can turn on GoogleMap while in Croatia, but I don't think it will work in Bosnia. Any suggestions?
Old-school paper maps have worked for me driving in many countries, including Slovenia, Croatia, and Greece (but not Bosnia). You can buy them in Europe or in advance, but look for the most detailed scale if you'll be getting off the main highways. See also http://www.ricksteves.com/travel-tips/transportation/navigate-european-roads.
We used a combination of our Garmin GPS which came with European maps and googlemaps directions which I had printed from home. We stopped at Pocitelj on the way to Mostar (from Trogir) and visited Blagaj as a day trip from Mostar (we were there 3 nights). The roads are fairly well signed. Be aware that there is often more than one road that takes you to your destination. Try to take the newer road as it will be more direct. faster, and probably wider. We learned this lesson first hand when driving from Mostar to Kotor. We also met people who said they bought detailed maps once they arrived in the area. Enjoy your time in Croatia and BiH!
Rather than waiting until you arrive, why not get a map from Amazon delivered to your home. They list quite a few, but my preference is for the Freytag and Berndt ones. The 1:200,000 Croatian Coast covers what you want I think.
You won't have any trouble finding any of those places. For one thing, you'll pass directly through Pocitelj on the way to Mostar and Blagaj is very near to Mostar (less-than 10 miles) and easy to find.
Split is a major city on the coast so will be very easy to find, just depends on what you want to see en route.
My best advice would be to familiarize yourself with Google Maps and look up directions to all those places.
We mostly used offline maps on our phones but had a paper map in the car. We found it easy to drive and navigate from city to city. I printed out turn-by-turn directions to each of our hotels but just looking at the offline map on the phone turned out to be the easiest thing.
I just got back from driving in Bosnia for a few days - all the way from Montenegro up toward Zagreb. I brought my Garmin GPS with me. I had bought the latest Europe map microSD card for it used on eBay. It worked mostly OK. The GPS map was definitely out of date in some areas. And the "yellow pages" information (attractions, hotel info, etc.) in the GPS map was awful for Bosnia. Once I asked it to take me to a specific hotel in a town, and it duly took me...to a completely different hotel on the other side of town!
But if you will be buying a SIM card in Croatia, why not just buy another one in Bosnia? That's what I did for my Android phone (which I could have used as a GPS too, but the phone itself is a bit slow). No doubt online maps like Google Maps will be much more up to date than any GPS map like mine you would buy. I bought a SIM card from m:tel from a vendor for 2 marks, and then I paid 3 marks at a news stand to recharge it to give me some voice calls + 1GB of data. That's about $3.50 USD - incredibly cheap. The cell phone guy activated the SIM card for me, but he could not get data to work on my phone. That required (once I got to Sarajevo) going to an m:tel store and having someone add a new access point into my phone so I could use data - took about ten minutes. After that the phone worked great for data, including occasional walking map directions via GPS. Next time, I'd probably use that instead of the GPS I brought with me this time.
Just did this. Did not have an app or a stand alone GPS. Used the map given to us by the rental car company. Did fine with that. When we got to Mostar, we had a little difficulty finding the hotel, but we stopped a couple of times and got directions. We had booked our hotel on booking.com and I wrote down the directions when I booked. We were fine.