So have moved stuff around (yes, again) and I’m pretty sure I now have the optimal layout for my existing furniture.
This leaves the area under the stairs completely free.
I don’t need any more storage, and I want some element of functionality, so I can only think of two things to do with it.
A. Have a day bed with shelves / decorations above for a kind of reading den. Could probably even fashion some kind of basic curtain to make it a proper den. But the only pictures I can find for this kind of thing are with fitted furniture, which I certainly can’t afford e.g.

This would fit for example
It’s a bit more modern looking than I’d prefer but I suppose that could be disguised with throws.
B. Have a desk for a study area. I already have a study in one of the spare bedrooms, so it’s completely superfluous, but then I have lots of seating already too 
I feel like I’m clearly leaving towards A, but I just worry it won’t end up looking anything like the images I have in my head with just standard free standing furniture
I feel bad that my dilemma is having too much space…