My three DC all have rooms approx 8ft x 6ft. They're all very different in layout.
DD (3) has a 5ft bed with a small table built to the end of the room along the end width. She can sit on the end of her bed at the table or on a little chair at the end (or a friend/ one of her brothers can sit there). Behind the bed she has a tree painted on the wall and the branches have slim shelves with ledges fixed to them where she has books and soft toys.
Along side the head of the bed to the door she has a 5x1 expedit then a 2x2 then a 5x1. Between the two 5x1's she has a clothes rail so clothes hang above her 2x2 in the middle. Above the clothes rail we're intending to fit a shelf to put her toys that are too big for the expedit squares. So she has 14 expedit squares plus a hanging rail for clothes, nappies, toys and books. We use five for clothes, one for nappies and the rest for toys. Under her bed she has a big pull out drawer for dolls stuff. The advantage of the expedits for storage is that they don't eat significantly into the room (about half conventional wardrobe depth) so theres plenty of floor space for play (considering its a small room)
DS2 (8) has a four drawer malm unit with on wall 2x2 expedit above then a micke desk that fits to the end wall with a double display shelf over for his model collections. He has a strip of floor down the middle of the room and then a sofa with very high bed over on the other side. The sofa is single bed size so doubles up as a guest bed, but is heavily pillowed to make it more comfy. (Less deep) to use as a sofa. The bed is custom built to give a comfy height sofa. (Two drawer full depth storage under for toys) and very high bed to create good head room clearence on the sofa. The ladder to access the bed is end wall mounted so it doesn't eat into the room space.
DS1 (11) has a narrower bed 80cm wide with a stuva wardrobe at the end. Over the bed he has a high wall mounted 5x1 expedit with storage boxes within and storage boxes ontop upto the ceiling. He stands on his bed to access these and its clear of adult head height when sitting on his bed. Again he has a narrow strip in the middle of the room then a very long thin besta burs (ikea again) desk with a stuva storage bench under and double display shelf above.
All three rooms work really well. We downsized from a house over double the size of the one we're in and its taken a lot of time to carefully design in the things we all need. Its been well worth customising off the shelf things to shoehorn everything in.
Lots of little things can make a big difference to the space you have available. Rehanging doors is worth considering if it gives you more layout options. I tend to sit with a sketch pad and draw out lots of different options until something works.
I spent a lot of time sailing as a child so i tend to think about boat layouts and use of space when i'm designing but caravan images are more readily available and if you look at just how much can be fitted into a caravan it can inspire some great ideas.
Those fold up beds are great, but as you say expensive. What about a set of narrow shelves with a fold down door that doubles as a desk to create floor space whilst having a fixed bed?