I did a week-long Yosemite trip late last August, I spent 1 night at the Tuolumne Meadows campground, and three nights backpacking (then two nights camping in the valley with my family).

The plan was to do a loop south of Tuolumne Meadows... heading SW down the John Muir trail through Cathedral and Sunrise lakes, up to Cloud's Rest, then head east through Merced Lake and back north via Vogelsang.

However, after the first day I changed those plans, because I got going late and wasn't making the time I wanted. I could have done the loop, but would have had to sacrifice Cloud's Rest which I really wanted to hit. So the first night I stayed at Cathedral Lakes, the second at lower Sunrise Lake, the third day I hiked up to Cloud's Rest then back to Sunrise Lake where I stayed again, and then the next day hiked out via Tenaya Lake (there's a regular shuttle that goes between popular spots around Tuolumne Meadows pretty often during the day which took me back to the wilderness office).

I ended up only backpacking for 4-6 hours each day, but it was much more relaxed and enjoyable. I was able to do a bunch of mini-day hikes out of each camp site when I arrived. I also have a ~50 pound pack, so I'm not going to do 20 miles a day anyway. I think I did 30 miles over four days... the last day was a quick hike out, so it was really around 27 miles over 3 days.

There were people which I expected since I was within day-hiking distance most of the time. The quietest day was the second when I hiked between Cathedral and Sunrise lakes, when I only ran into 6 or so people while hiking.

Elevation wasn't a huge issue, and I'm a smoker who lives at sea level (although also only 28 years old). The first night camping at Tuolumne probably helped, and the second day on I felt great (first was a little tough).

Cloud's Rest was absolutely worth it, and the lakes were beautiful.

Here's a good map if you haven't seen it yet:

https://snri.ucmerced.edu/snri/wawona/download/YOSEMITE%20map.pdf

Also, my best advice is to buy your own bear canister (or at least give yourself time to pack a rented one), unless you're really good at carrying minimal supplies. I had a tough time fitting everything I needed (or thought I needed) into the one I rented, and would have rather had it at home ahead of time so I could practice packing it.

Edit to add:

Check reservation dates... they open months early and sometimes reservations sell out quickly, especially for campground sites. If you can't get a reservation for wilderness permits you're not completely out of luck, they save half for first-come first-serve, but if that's the case have secondary trips ready.