I am indeed a weekend warrior who only plays for an hour or so most days, and only about three hours straight ever. People who make a living playing probably play as much in a day as I play in a week or more.
I'm actually more concerned about what happens to my left hand, and that's why I like having the neck in as vertical an orientation as possible. A vertical neck means neither wrist is bent much, at least for me. It means anchoring doesn't result in much wrist bend. Having the bass slung low bends the left wrist a lot while allowing the right wrist to be straigher. High is the reverse. Vertical allows both to relax. I suppose you could use a slap technique with the bass like that, but I sure can't. The rare times I slap require the neck to come down for a while. Then it goes right back up.
Sounds like you are a perfect candidate for an upright bass. I had an electric (NS NXT 4 string) and it was on an adjustable stand that you could set at the perfect angle so that no strain was put on either wrist and it was a pleasure to play. Damn...now I'm sorry I sold that bass! I think you would like one of those.