I ended up going to Cabo after all, but I will definitely keep everyone's great suggestions in mind for my next trip! I went with Cabo because there was a very cheap ($250 round-trip) flight with the exact departure and return times I wanted, which I didn't have for any of the other places I looked at. I also found a dive hostel for $22/night, which made the whole trip logistically very easy and economical.
The diving was pretty good, to my easily-impressed newbie mind. I got up real close to a bunch of sea lions, which was freaking adorable. Decent number and variety of other critters too. Visibility was fine, not amazing, maybe 20 feet? I'm still learning how to judge that. Water was in the low 70s, a little warmer than it ever gets here in LA so quite pleasant to me. I managed 7 dives over 3 days with a comfortable margin for flying home on the 4th day. My total dive count is still so low that I seem to be having at least one "first" with every dive, and my skills are noticeably better and my confidence is up since before I went on this trip. So, all in all, it was what I was looking for.
Would I go back? Maybe. The dive hostel was an interesting experience. I kind of knew what to expect as far as the facilities. I've stayed in plenty of hostels before, though not since my twenties. I hoped since this one was geared toward divers, the guests would skew a bit older. I was right; the other guests all seemed to be in their thirties too, so I wasn't that weird old person at the hostel I used to side-eye.
The guy who runs it, though, is a bit of an odd duck. He insists the water there is saltier than anywhere else on earth except the Dead Sea, and therefore tries to get everyone wearing 5-10 lbs. of extra lead. (He arranges equipment rentals and boat dives for guests at an extra charge.) He told me I'd need 20 lbs; I told him no, I use 20 lbs. when I dive with a 7mm, and he had me in a 5mm. He insisted I try it, and besides, he only had 4 and 5 lb. weights, so I'd have to go all the way down to 16 lbs. if I wanted less. That seemed like it might not be enough, so I agreed to try the 20 lbs. I did a bouyancy check in the water and sank to a little below eye level while holding a normal breath, so I figured I was a little overweighted but didn't think taking off 4 lbs. would be a good idea.
But he thought I needed even more weight. I told him no, I was fine. He wanted some more weight on his tank, so he asked me to turn around so he could demonstrate to the other diver in our group (who was training to be a DM) how to put the weight on his tank strap so she could do it for him. Apparently he took this opportunity to add another 4 lbs. he thought I needed to my gear, though he didn't tell me this until later.
When I deflated my BCD I sank like a stone and immediately resolved to try 16 lbs. on the second dive. I struggled to get off the bottom; even in my OW course they didn't overweight me, so I've never needed more than a squirt or two of air at a time. We changed depth a lot swimming over the reef and I couldn't quite keep up with pumping and dumping so much air, and the stress and finning up and down was making me breathe harder. When we did our safety stop over a sandy bottom at 10 ft. I struggled to vent my BCD, because of course the air didn't want to come out very fast when I was horizontal but I was this close to popping my head or feet up if I got vertical. I was trying to use the dump valve on the bottom right side while finning head-down, but he insisted on "helping" me get head-up and using my shoulder valve. Whatever, I'm sure I looked like I was totally failing at life in that moment and can't fault him for wanting to intervene.
For the second dive, I told him I wanted less weight; that's when he told me he'd slipped another 4 lbs. in my trim pocket and said I should now try 20, which was what I thought I'd had before! I did, and it was still too much. It ended up being this whole bizarre confrontation the next day when he tried to deny that he'd ever said he'd added more weight behind my back, then admitted it but insisted it didn't matter because none of the weights were true anyway, and got super defensive saying he's never had this problem with anyone else before. I was about to just bail on my last day of diving because I didn't trust this dude, when he apologized and promised not to do it again, and to give me exactly the 18 lbs. I wanted.
Sometimes I wish I'd found a way to get into diving sooner, for obvious reasons. Other times, like now, I'm glad I waited till I was 35 and had used up all the f***s I had to give in these kinds of situations. Ten or fifteen years ago, I might have let this guy push me around and gaslight me. I would have had somewhere between a stressful and a miserable experience, possibly injuring myself, for fear of being the only person to ever give him such a hard time. Now I feel like, if I really am the only person who hasn't gone along with his BS, I've done a public service.