"You still haven't said why a loft extension isn't possible when so many bungalows have them."
To those who keep suggesting that OP extends the house or converts the loft, aren't you assuming that she owns the house. I don't think she has actually said whether she owns it or rents it.
If it is the case that it is rented then OP does not have the option of converting or extending.
Certainly, I'm making my own assumptions here, as I think Pompom rents the house, choosing the option of a small detached bungalow with a garden (rather than, for example, a less expensive but larger terrace house with very limited outside space) because she needs the shed, which she has adapted as a tiny music studio, which she needs in order to earn a living.
That would be a rock and a hard place, move to a bigger property but be unable to earn a living, or stay in the smaller property meaning a bedroom must be shared.
I'm probably wrong in my assumptions
, but either way, if OP doesn't want to explain her circumstances then we simply have to believe that she cannot move and cannot extend, so a solution has to be sought within the boundaries of those things.
Lots of posters have offered ideas that would work within that.