Ironically my recent new HT purchasing requirements were very similar to yours RD. Although I’d have preferred 142×12, it’s not a deal breaker, and I wasn’t fussed about 27.5+ (though it does fit, I’ve tried it), I bought a…
Whyte 629
Annoyingly it’s not available as a frame only, but it’s a cracker of a frame. The geometry charts are, if anything, a little conservative, as with a 110mm Reba in place of the 100mm Recon mine has a measured HA of 67 degrees. Very long ETT for its size means nice short stems, low (threaded BB) height, 440mm stays aren’t super short but they’re short enough, and the bare frame is under 2kg in a medium size. Add in plenty of tyre clearance with normal 29er tyres, a 30.9 seat tube etc. and jobs a goodun. Only issue is that it’s not available frame only!