Can you help get rid of the mud? Studio Design help needed

Hi I create and mix my music mainly in a small 1 bedroom flat in Sydney Australia. The studio also pretends to be a living room. At the moment Im getting a lot of mud around the 200-400hz area - bass is very loud in the room corners and dead in the center. When playing bass notes on a synth certain notes resonate a lot louder than others! Compared to other places Ive mixed, my results here are not so good...so thats where I need help. Im not the greatest mix engineer around, but this space isnt helping me much... I went to a place called the "Foam Booth" today. They sell 50mm deep Acoustic foam for a reasonable price... and there was also some 4" deep high density foam that i thought might work to control the bottom end if placed somewhere. I havent found any reference to this stuff anywhere on here. Its a solid foam (no dimples) and I thought it might work of placed in large flat slab sections on the walls and the corners... I've got $1000 AUD (or near that) to try and get the problems sorted. Im also happy to shift things around a bit but the possibilities are limited due to the many doorways, my girlfriend's patience and the overall lack of space. I liked the look of the high density foam because a) it was easy b) if I brought home a stack of wood and a roll of fiberglass insulation my girlfriend would probably move out. The foam has the option of being removeable...which is good from her point of view. The floor is carpeted, and as Im on the 3rd floor of an apartment I dont play my music loud (sorry - that is a subjective comment)...but I do generally keep it down. I often mix with one speaker (in mono) ... I read somewhere this can help mixdown in a bad room... The walls are brick, covered with plaster (then painted) (Bulding is from the 1920s), with a wooden picture rail around the room. Im not recording/ tracking anything in this space - its purely for mixdowns inside the computer. If theres anything else I can provide to aid anyone helping me - please ask! I havent done an elevation of the desk area (it would need to be quite detailed) ...if you need one...I'll do it. Also - these jpgs are available as .eps or Adobe illustrator files Thank you Royalston ps. sorry for the previously large files...I the the files 750 pixels wide....but they came out huge!

If theres anything else I can provide to aid anyone helping me - please ask!

yup - resize those huge pics so I can see the page without having to scroll right!!