26″ straight steerer 150mm.

Any good QR forks? Or is it worth spending more and getting 15mm wheels?

Do you really mean straight steerer? You’re going to be struggling to get much with a straight steerer and may not have a choice of axles when you find one.

Yes. Bfe early frame

Old marz z1s?
Old lyriks?
Newer, but still old revs?

Revelations from eBay, though you may have to look at 140mm.

Reckon you could get them for ~£100, just be patient

Or possibly Recons which would probably be even cheaper

Older fox units or even a new fox fork although you’d be bending over for that one.

Something on ebay? I would say going 15mm would make things easier can your hubs cope – plenty do very easily