Mountain Equipment Fitzroy. I tried on a bunch of synth belay jackets, settled on this for fit (ME has gone slimmer, Rab has gone tubbier since I last bought. Sounds like the temp range you’re after.
And it turns out Fitzroy insulation is now Hydrophobic down. win-win.
Warm but not ridiculous, so possibly what you’re after. It’ll take a light shower. It’s got a hood, but I like a hood, cos I’ve got a baldy head.
Take care if you’re buying, they’re available from £100, but you might find an older one with the Primaloft One synth insulation. You want the Primaloft Gold, 90% hydrophobic down