What about potatoes? In their skins and if you can eat their skins as that's the bit that is full of protein. Mashed including their skins is good. Good with poached egg or scrambled egg.
The scots used to have the best diet in the world, oats which presumably you can't have, kale, potatoes and mackerel or herring. Ie oily fish. V cheap. A herring in our local Tesco costs about 70 p and would do two meals for me, grilled or made into a potato based pate equivalent ;a tin of sardines or mackerel or cods roe from lidl will do likewise.
Can you think Japanese too? Sprouted beans, veg and rice ? Tiny bit if other protein. As and when your digestive tract strengthens, try brown rice as has more protein. Even just drinking the water it has been boiled in will help.
Could someone lovely give you a bottle of nice olive oil? And some compacted coconut to make coconut milk from for curries.
Puréed carrots surprisingly add fullness to soups and veg stews. There is an Italian soup that is clear broth with rice and egg, you can ring the variations with carrots, puréed are easier to digest. Broth can be made either using a stock cube or by boiling a chicken carcass once you have eaten the flesh.
Does offal turn you off ? If not, the Italians do wonderful recipes for it and it is brilliant for iron and easy to digest. And mostly v cheap. But avoid anything from a pig, v strong tasting.
A boiled egg with soldiers or soup , followed by a baked apple is a really nice supper, or so I think.
If you have a thermos, put dried chickpeas in boiling water in it overnight. Afair they soften and the skins come off.
Do you have a window sill ? See if you can find a pot and soil and grow your isn lettuces. And cress on an old flannel.
Good luck. You are brave.