If you keep riding your bike, you'll gain stamina and strength. Personally I like the thinner saddles as the thick cushy one caused pain in my sciatica. Getting used to the thinner saddles is really just a matter of spending time in the saddle. In other words, riding.
I go through phases of riding a lot and then going on to something else for a while. We've been trying to minimize car use so starting June 1, we began to bike for as many errands as possible. (I logged about 170 miles on the bike last month.) DH even got an Xtracycle and built a trailer so we can avoid using the car just because we have a lot to carry. We had 3 CSA shares to bring home last night (one for a friend) and he hauled the following in the Xtracycle bags and an icechest on the trailer:
1 watermelon
2 Canary melons
3 spaghetti squash
4 cucumbers
10 tomatoes (more than our share because I brought home the bruised ones to salvage)
12 potatoes
9 ears of corn
2 crookneck squash
2 zucchini (one almost baseball bat size)
Guess I'll be eating southwestern type food this week! (Picture and menu will be posted on my blog later today.)