My family and I spent two weeks in Slovenia this past July, you can check out the places we went to:
https://community.ricksteves.com/travel-forum/trip-reports/slovenia-14-days-13-nights-road-trip
Considering what are important to you:
do not want to rent a car.
cannot do long hikes but we would love to see beautiful area
drink good wine and eat good food.
like staying at a hotel for 2 to 3 nights. I do not like 1 night hotel stays.
easiest way travel between these areas with public transportation, taxies etc..
"Day 1,2 Ljubliana
Day 3, 4, 5 Lake Bled
Day 6,7 Lake Bohinj
Day 8,9 Kranjska Gora
Day 10,11,12 Piran or is Izola better...we love the coast
Day 13 Ljubljana to fly out the next day."
Here are my thoughts:
Both Bled and Ljub are about 20-30minutes from the airport, maybe it's more efficient to go to Bled directly after landing by taxi.
Lake Bohinj is pretty, but Bled is bigger, has more dinning options within walking distance, it is a hub with tour companies at your disposal, better public transportations etc. A private guide with car would be nice to go to hard to reach/off the beaten track areas.
For amazing view with minimal physical effort, try zip lining, there are many companies doing this.
With 5-6 days in Bled, you have two days exploring Bled area, a couple of days for organized tours/guide with transportation included. Soca valley is beautiful.
Kranjska Gora is resort town for winter sports, we drove by it without stopping.
There are companies do tours leaving from either Bled or Ljub go down south, stopping at Postojna cave among other places and end the tour at Piran.
Once at Piran, a private guide with a car can take you to Slovenian wine region for some wine tasting.
Finish your trip at Ljub for good food, walking around, maybe more organized tours...
We did not notice any thermal spa where we went. The true thermal spas are mostly at the east region of the country.