HF absorbtion

Hi :) Im having a problem now Ive started to make bass traps. Most of the muddiness of my bass is going away every time I add a new panel but Im having problems with high frequencies (Id say 7/8k and above). When I stick a trap infront of my monitor and turn the other off it absorbs everything very well other than highs - so Im looking into treating my room further to get rid of this problem. When I mic up the reflective surfaces my mid wall and ceiling seem to have it worst (as I would expect). My mixing position isnt the most ideal but Im not just in a home studio - Im in a bedroom studio! The dimentions of my room are 4.2x3.5x2.8. Im mixing facing the 4.2m wall which I know isnt ideal but I have numerous closets and radiators and a massive window that mean I cant face the other way. My speakers sit at exactly 1/3 of the height of my room if this helps. I currently have 1 massive trap 4inches thick made from fibreglass insulation with a wooden frame and covered in cotton in my corner (thank you for the guides btw guys :)). Ive just made 2 for the ceiling - although I may position them elsewhere. Part of another 2 of my corners are revealed (both have doors in the bottom half) and Im making the traps for these tonight. Ive mainly been looking into foam but if you guys have anything pretty easy to build that would help me that would be great. Tell me if you need more info or what I missed out

Foam , rockwool they all are HF absorbsers.

What shaping and thickness of foam is best?