Head over to GearSlutz, and navigate to the "Studio building / acoustics" forum, and then go to the "Bass traps acoustic panels, foam etc" sub-forum. There are lots of DIY examples there. You will probably want to modify somewhat the examples you find there for stand mounting, but if you're handy, that should be do-able. Here's a classic thread:
https://www.gearslutz.com/board/bass-tr ... traps.html
Note that although the title of the thread above says "bass traps," if you omit the FRK/FSK facing, they become broad-band absorbers.
A room that is too dead is not good either (as FriFlo said), so you might want to make some diffusors:
https://www.gearslutz.com/board/bass-tr ... fuser.html
Note that this GS forum and its parent forum have tons of good information on studio design and acoustics, as well as measurement and treatment options. The one thing to avoid (and it looks like you are already planning to avoid it) is putting thin "acoustic foam" tiles or panels everywhere; these tend to absorb highs dis-proportionally and leave the room swimming in low and mid frequencies. It's a shame that "foam packs" are marketed so heavily when the often make the problem room (arguably) worse when they are not intelligently combined with bass trapping and diffusors.
