Thanks for the update! Sorry things haven't improved...but you're hanging in there! It really sounds like he (and you!) would do better if you could wear him around a bit. I mean, I know the ultimate goal is to be able to set him down for a few minutes, but if you're carrying him around all day anyways, you might as well find something that lets you be hands-free.
There are wraps and carriers. Everyone (and every baby) is different, but I always preferred carriers, even for newborns. It just seemed easier to plop them in and take them out easily when necessary, without a lot of wrapping and adjusting. There's are some websites where you can "rent" them - just to try different ones for a little while and see what works best, so you don't waste a lot of money. FWIW, I LOVE my Boba carrier. I had my newborn in there without any sort of special insert or something. I'm sure I used it when she was just a few weeks old. Even with her floppy head, it kept her in there nice and snug. Ring slings can be good, too. Just some thoughts. I wish I had some magic answers for you!
I'm sure others will chime in, but it sounds like his weight gain is just fine!