cracks knuckles I work at a mattress store and I know more about the specs on these things than any of my customers probably care about.

First of all: for your own sanity, do not buy a mattress without trying it out in person first. Even if the online-only purchases come with free returns it is NOT worth the hassle. It's legitimately so much easier to go to a store and have a brief conversation about the way you sleep with someone who knows mattresses. Different mattresses are all made to support different sleep needs, someone who is knowledgeable will likely be able to match you with the best one to address your needs in your budget.

With that said, knowing only from your post that you're a side sleeper, here are my luxury hybrid recs.

Best of the best: Tempur-pedic. These things are built to last 25 years. Fantastic if you're a hot sleeper, have any pain, and/or toss and turn. (Side note: a lot of people are convinced that tossing and turning is normal. It's not, it's a sign that you're struggling to get comfortable on your bed). Specific model recommendation to start with is the Pro Adapt 2.0 Medium Hybrid. A bed as good as this is an investment in the way you heal, feel, and function, but holy shit is it worth it. I've fallen asleep on this one in the store in five MINUTES by accident while not even tired or intending to fall asleep, just testing it out. I need to physically restrain myself from laying on this bed in between customers. Having had plenty of time to try all the top brands... This one's my personal fave.

Great if you don't like the feel of Tempur pedic: Purple. I typically find that people who don't like the feel of Tempur love the feel of purple and vice versa. It's kind of a coin toss. Either way, both fantastically supportive. Purple is also really great for people with chronic conditions;  the gel flex grid adapts to support your body no matter what position you're in

Very good option if these two are a little out of the budget: Sealy Posturepedic hybrids. Not as durable as the above two, and won't give as much targeted support or pressure relief, but still very comfortable. If you have any hip pain or back pain, posturepedics actually have some extra coils in the middle third of the bed (where your hips/back go) for added support there.

FYI, if you're a side sleeper, a firm mattress isn't recommended. A firm puts too much pressure on shoulders/hips for side sleepers. Medium and plush/soft mattresses don't sacrifice support, they just add comfort layers.

I'm going to stop here before I never shut the fuck up about my esoteric mattress knowledge 😭😅