Keep thinking of other things...
Bristol - got an interview offer from them, but didn't attend (uni wouldn't have been right for me for various reasons). Nonetheless, I did speak at length to a tutor at my college who'd been there as a mature student and loved it, but that's hearsay evidence, of course.
Cambridge - IIRC, lower income applicants are given priority for places at the Mature Students Summer School, but if you're accepted onto it, it's free. Oxford's equivalent is quite pricey, I think. Cambridge also offer an enhanced bursary for mature candidates who live in the area year round, i.e. aren't going back home elsewhere during holidays.
Imo, the fact that Oxford and Cambridge offer mature summer schools and mature colleges at all does put them both up at or near the top of the list in terms of their mature-friendliness, even if Cambridge perhaps has the edge. How much of an advantage the additional bursary is at Cambridge would also vary according to the applicant's circumstances. I believe Oxford offer reduced tuition fees for those on a low income; that might work out better for some.