Can a slim person have the same mattress problems as a heavier sleeper?

Same weight range. My issue was the mattress was too soft on top but too firm underneath. Felt like sleeping on a stale marshmallow over a brick. If you're light, you don't compress the comfort layers enough, so you just perch on them. The support layer underneath becomes irrelevant. That might be your 'hitting something hard' feeling.

This is going to sound weird but have you tried sleeping on the floor for a night? I did that once out of desperation and the back pain vanished. That told me my bed was the problem, not my body.

No, you're not crazy. I'm 115 lbs and my old mattress was a 'medium' that felt like concrete. Turns out I was too light to even engage the top foam layer, so I was basically lying directly on the pocket coils. Swapped to a soft latex topper and it changed everything. Not saying that's your fix, but you're definitely not alone.

The whole 'light people need soft, heavy people need firm' rule is based on averages and honestly it's kind of useless. It ignores how you sleep and your body shape. I'm 160 and sleep on my stomach and need something way firmer than my 220 lb side-sleeping buddy. Weight is one factor, not the factor.

medium-firm is a markeing lie anyway. Every brand defines it differently. One company's medium-firm is another's extra firm. That's probably half your problem right there.

Pillowfort is right. I ordered a 'medium' from one of the bed-in-a-box brands and it was softer than my grandmother's antique guest bed. Sent it back.

What's your sleeping position, OP? That matters way more than your weight honestly. Side sleepers need more give at the shoulder and hip. Back sleepers need more even support. Stomach sleepers need firm. If you're a side sleeper on a medium-firm that doesn't give enough, your lower back will absolutely scream at you.

Also how old is the mattress? 'Only 2 years' can still meaan it's shot if it was cheap or if you never rotated it.

The floor hack actually worked for me too. Slept on a rug for 3 nights while waiting for a new bed and my back felt better than it had in months. Humbling.

I'm a bigger guy and honestly I think the mattress industry just wants to sell you two things: a mattress for 'heavy' people that's basically plywood, or a mattress for 'light' people that's a cloud. Neither works for everyone in those categories. It's a mess.

Also worth checking if your mattress has a zoning issue. Some have softer foam in the middle for pressure relief but if you're light, your hips don't sink enough to hit the support zone, so you end up in a weird hammock position. That can absolutely cause lower back pain.

Honestly at 130 lbs a soft latex topper is probably the cheapest thing to try before buying a whole new mattress. $100 experiment vs $1000 mistake.

Toppers are tricky though. A soft topper on an already-too-soft mattress can make things worse. But on a mattress that's too firm underneath, it can help. It's a band-aid at best.

This thread is making me realize mattress shopping is basically astrology for your spine. Nobody actually knows anything. We're all just guessing and hoping our backs don't hate us in the morning.