I think my problem is different -- I am trying to dress my loungewear up, in a sense!
What I mean is that before YLF I had taken to wearing my workout wear around the house at all times. That was my "loungewear." And my everything wear, too. I had a few other pieces, sure, that I wore for special events or going out. But not a heck of a lot.
I still spend most of my days at home, (apart from frequent travelling, that is...) but because of this, I decided that I wanted to wear real clothes at home vs. loungewear, at least most of the time. The only thing is, I want my real clothes to feel as comfortable as loungewear or gear. And at the same time, they have to look fashionable, so that if I end up going out, I only have to add a third piece of some accessories to make an outfit. Rather than changing altogether.
Anyway...enough about me!
I love that blue on you; it is just stunning!
As for the fear you won't wear your loungewear if you buy new, the simple solution is to purge the older, less fab stuff. Then you won't have a choice! Really, when things are worn out, they need to go. And you deserve something new then.
Another solution, if you find a sort of jacket thing of this type useful, is to have two of them in rotation, so you won't run into laundry difficulties. It must be washable -- otherwise, forget it. Also, if you think a pattern would be more practical, you can look for that. But I don't see why it inherently would.
It sounds as if you have identified some features that make a piece work for you, though. So why not go with your hunches on this? We all have different needs and priorities and preferences when it comes to this kind of personal wear, and since you don't need to make a fashion statement but simply comfort yourself and make it easy to move around (and get cozy...or cool, depending on the season) it really should be up to you.
For myself, at home (as opposed to out in the world) in winter, I find I wear: soft knit tops (jumpers) not wovens. Sleeves I can push back a bit. High necks or scarves. Pants with either stretch or loosenss. Warm socks.
In summer: more woven tops, long shorts or loose light pants, bare feet.
So, after a year of paying close attention, I can now buy for my work-at-home wardrobe in some confidence that what I purchase will actually work for me. Meanwhile, I have other criteria for the clothes that I wear out in the world. There is obviously some overlap, as that is the whole point of this capsule for me. But there needn't be for everyone.