Fox, you carry stuff for your Mrs ???? My hubby and I share, each according to our capacity/ability. I wouldn't have it any other way.
I remember an incident in the Pyrenees meeting loads of French hiker couples - guys weighed down under enormous packs, their partners tripping along with little day packs - my pack looked every bit as big as my, much bigger, hubby's pack - The looks of awe from the French was a great ego boost . German women wouldn't let their men carry their stuff either.
A Zpacks Soloplex isn't going to 'cut it' on some Scottish summit in wet hoolie. A 30l pack isn't going to be big enough unless the rest of your gear is much smaller/lighter. Only you can know if a Cumulus 250 bag will be warm enough for you and what you do - I would freeze unless it was high summer.
Change one thing at a time. I suggest you start with investing in a good quality down bag. I buy a lot of stuff as 'nearly new top quality' - If I make a mistake I can sell on without too much of a loss.