"Gobos" will bring up a bunch of designs if you search it.
This post suggests a depth that would work for your case i think, getting down to 80hz will grab the open E string in standard tuning.

Can a 3' inch rockwool acoustic panel be used as bass trap


I would build enough to completely surround you or surround you 3/4 of the way around ie front and sides, and try and setup away from the walls, but not dead center of the room.