Very feasible. Pretty much what I did after leaving my previous course (engineering) for mental illness reasons also (albeit somewhat different conditions), and I'm now studying a humanities course at UCL. I didn't bother going back and doing A-levels, I did a CertHE course at another uni in a related subject, although this was mainly possible due to COVID and everything being remote for me. I would have otherwise probably looked into an Access to HE course rather than A-levels (and this is probably a better option than a CertHE as that can complicate the funding situation further potentially).
Universities are happy to receive applications from suitably qualified mature student, no reason not to if you can figure out the funding side of things. You may not have funding for a full, full-time course left, unless you apply for compelling personal reasons (which sounds reasonable in context but you'll probably need documentation from the time as well as now to support that). Bear in mind if you're going to stop working for the course to plan your finances accordingly also. This is I think for most mature students (particularly those in career level roles already) the biggest potential barrier, but it's ultimately a personal choice.