Shelf recommendations?

Giving the shelf support in the middle is your best bet - or putting a reinforcing cross piece perpendicular to the shelf. With modern mass produced shelving being almost exclusively "engineered wood" (MDF/particle board, in other words sawdust and glue with a plastic veneer that looks like wood grain) there isn't much you can do! I have had good luck finding real wood shelves at Cost Plus World Market and Pier 1 Imports, off and on, but shipping is not possible as they are almost always pre-assembled.

Recently I wanted a quick and cheap shelf unit for overflow, and I went with the below: still engineered wood, but each shelf has a cross-piece across the front that provides excellent support.

https://amzn.to/41okvJW

Good advice Urulókë

If you are looking for cases that are solid wood and don't want to break the bank. Depending on where you live, do a Google search for antique stores in your area that have vintage furniture listings. You may find some cases that are sturdy and well made and can be had for a few hundred dollars. I have found two lawyers cases (solid wood, glass doors) over the years this way.