I'd hold off on the powerline, they can cause interference with VDSL and with it being so early I wouldn't want to risk the line getting banded. At the very least, make sure they have a VDSL mode which is supposed to avoid using the same frequencies.
Is there no possibility of adding a physical ethernet cable from your booster back to the router? Its a hassle, but its the only guaranteed way to get the speed and stability.
No, there's no chance as it would need to go through two walls. I have tried moving the booster around but essentially there are trade offs with doing that. I've been unable to move the booster to a place so far where it gives a reliable Sky Q TV service and also a decent wifi signal to the office area.
As stated previously I am currently at my fathers caring for him whilst he waits for the second part of major surgery delayed by COVID and running any cable in a place where it could be a trip hazard etc is a big no no.
I read about interference from Powerline adapters but it seemed to be pretty much that some people are effected by them and some people are not. Could I potentially sidestep this by moving the booster to a place where it gets a fairly good signal, but still not close to the main router, and plugging powerline into that rather than the router directly, or will that still cause interference?
I've tried the booster in two different spaces today and I've managed to get really really good connection to the mini box and in the hall (about 60-70Mbps) and two bedrooms upstairs but 15Mbps in the office. If I leave it in the current place where it's always been, I get about 30-40Mbps everywhere.