So you buy a nice two shelf bookcase but it’s wobbly and you know it won’t hold much. I’ve recently gotten one and my solution was to put L-brackets on it. After installing about 8 of these brackets at the cojoining parts of the shelving, it is now completely stable and ready for use.
I’m pretty happy with the combo of a cheap, thin mattress with a nicer memory foam topper on it. Affordable, and can replace the topper separately if needed producing less waste than needing a whole new mattress.