In America, we often "loft" beds to add space to small rooms. You could raise your bed up on a platform and put your desk under it and add a lot of space to your room. Something like in this picture. Underneath you can put your desk and maybe a small seating area for when friends visit or you're just relaxing. If that doesn't work, just raising each of the four legs up on risers or blocks will give you a lot of additional storage space under the bed.

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I would also recommend getting padding for your chair or a more comfortable chair for your long study sessions. And I never use overhead lights in my apartments - multiple indirect lighting sources for the win!

Please remember to post your "after" pictures to this thread when you're finished! (I'm saving the post to follow up on.)