I’ve never done trips even remotely as challenging as you’re planning, so I’m not offering any expert advice, or anything even close.
I did do some quick browsing in tents, and might suggest you take a look at the MSR Access 1 one-person tent - it’s billed as four-season and weighs 3 or 3.5 pounds. I’ve used MSR three-season tents for a long time, and really like them. They also have two and three person tents listed as four-season.
I’ve also had good luck with Big Agnes tents; their website also indicates they have four-season tents (“mountaineering” is the term they use.) The only thing they offer for one person is the Three-Wire bivy (which might interest you); their other “mountaineering” tents are all two-person. Theirs are four pounds or five pounds - but they are two person. The extra room might be something to consider, considering the amount of gear you’re taking and the amount of time you might spend in it.
Good luck; it sounds like a great trip.