@AliK....Sorry, this is going to be rambling but just glanced through some of your posts and we've all been exactly where you are.
There are so many things which are almost impossible to explain to people who either haven't been through a knee replacement or have had to live with someone who has been through a replacement. My husband has been very supportive and great through both of mine and still says he can't imagine what it's like to deal with the pain, etc.
After the initial pain and shock of surgery, the ongoing exhaustion is another thing people just simply don't understand because you don't look "sick". In fairness, 4 years ago, I wouldn't have understood why someone with a new knee couldn't (for example) stand in line for 5 minutes (which is my limit) or why there are shooting pains through it, etc. But I also would have never asked someone why they were or weren't doing "so and so" so it's annoying when I'm asked things like why I'm still using a cane - but won't go off on that rant here.
Insofar as regretting not waiting to have this done....don't waste your energy on regret. I put off having my first TKR much too long for a variety of reasons and my knee deteriorated badly very quickly. My husband talked me into having my second one sooner rather than later (the day before yours) and I'm so grateful he did. The recovery from this one hasn't been a piece of cake but it's been much, much easier than from the first one. If you'd put it off, then you'd be that much further into next year before you felt better - and who knows how bad your knee would have gotten in the meantime.
You're doing a great job by getting back to work, etc. Don't pay attention to everyone else's opinion unless they've had a replacement; otherwise, they don't know what they're talking about. If they insist on making comments, suggest they watch a video of the surgery; that might encourage them to keep their opinions to themselves.