Sounds like you have quite a few opportunities for sitting. If you're like me, you're quite attached to your pretty but impractical high heels. I wouldn't be clamoring to put them up on eBay just yet, unless you want to increase your budget for new shoes with lower heels. It's not like you can't wear them AT ALL. If that were the case, even looking at them might make you feel sad and frustrated -- but you *can* wear them, if you choose the occasion carefully. And I imagine you like variety in your shoe choices.
If it were me, and I had come to the realization that I could only wear high heels for sitting occasions, I'd still keep the six pairs of three-inches-or-more heels that I currently own, because I really love them all and they are quite different. But I probably wouldn't try to acquire any more.
ETA and for what it's worth, none of us is supposed to wear sky-high heels for regular every day wear, anyway. It's all kinds of bad for the back, as you well know! I get a bit of sciatica now and then and I try not to aggravate it with lots of charging around town in high heels.