Looking for recommendations for a cheap mattress that’s fiberglass free

I'm looking to replace my current horrible mattress, after trying to make it work for years with a memory foam topper that just still doesn't make it comfortable. But I don't have much to spend. I'd definitely ideally like to find something that's fiberglass-free too, and probably about medium firmness

Does anyone have any <$500 mattresses they'd recommend, without any fiberglass? Ideally I'd like to order one online, Amazon or somewhere