Hello
We just got back from a fortnight in Istria area. Beautiful!!!
You can base yourself in Pula and visit the many parts of Istria from there. Also, from Pula, a boat (catamaran) Bisovo goes to Zadar every couple of days. We’ve used it to go to the island of Unije. You can get more details from tourist agencies in Pula, especially the ones in the port. You can use buses to get to Rovinj or Porec. There are plenty of things to see, but it is easier with the car.
Hope this helps and let me know if I can help you further.
Cheers
AmberMaria