Welcome Michele you'll get loads of support and ideas from this group. Looking forward to seeing your posts

This is a very friendly group, welcome! Don't worry about looking silly. Let the lifeguard know you're new to this pool, and let her/him recommend a lane. I always ask another swimmer before sharing a lane, even though it is expected, it never hurts to be nice. Make a point to say hello to the lifeguards everythime you go, and the chances are they will get to know you and keep an eye out to make sure you're getting along well in your lane.

Swimming is such a great exercise and especially for the problems you described. I have degenerative disc disease in my low back and it’s been the best way for me to do some exercise. I also like to hit the hot tub after. I go to my local YMCA and they have an app that tells me how many lanes will be open and at what time. I’ll go in the afternoons. Everybody is at lunch at noon and the pool never seems to be busy then. Best of luck!

Don't be afraid to say "hi" to other swimmers. Talk to folks in the locker room or hot tub. If you get to know someone else who swims around the same time as you, even if you swim at different speeds, if you can share a lane successfully you are an asset to each other. I've seen people hold the other side of the lane on busy days. i.e. if they see their friend on deck and someone else asks to share, they tell the other person they are waiting on a lap buddy and point to the friend.
Pay attention to what people are doing for their workout when you lane share. If you see someone doing a fly set or a breaststroke set & other lanes are open try those first, unless you are doing a similar set too. Yes, it is etiquette to lane share, but sharing goes both ways, everyone want to get their workout in injury free. I freely admit I can be kind of a *kitten* if someone just jumps in with me and I have to scrape my plan for a workout or they hijack the lane. I will share a lane with anyone who doesn't try to drown me. I have a few people I don't share a lane with because they tend to do wave crashing drills while I streamline kick on my back.
The "regular" folks at my pool, mostly, know I have my workout on the dry erase board. I shared a lane with a guy last week and I switched my last 300 from 12 x 25 IMO, to 12 x 25 IMO kick so I wouldn't bowl him over on a 25 sprint of fly, as soon as I finished the kick set he moved to another lane. After my cooldown he apologized because he didn't see my board at first & he had moved so I could do my intended set. I would share a lane with that guy again.
Another thing I try to do to be nice, if I get close to the end of my workout and I see you on deck I might say "Hey, I've got 5 more minutes if you want to warm up while I cool down you can have this lane." "Or I have 3 working minutes if you want to share". Sometimes they jump in or they might decide to fill their water bottle or do dry land stretching while I finish up.