I've only used a couple of blinds over the years, starting with a tipi blind I built with bamboo poles and fabric, 40 years ago.
All the advice has been very good - you need full coverage, opaque fabric, dark clothes, etc. You may have to cover your face, like me, you look pale with gray/white hair and any light bouncing into the blind could light you up like a spotlight. Some birds are particularly wary and some kind of face covering will help, as will dark gloves. I use a hunter's camo face net with one eye hole cut out, a dark hat and, sometimes, anti-glare sun glasses, too. All from Cabela's.
I found that fabric blinds deteriorate rather quickly and mine have only lasted a couple of months outdoors before the fabric became so weak that almost any touch to move or adjust the blind punched holes in it or the ribs worked their way through. It would probably extend their life, if you use an easily replaceable cover to get the sun off it. I'd use spring clamps to attach it or something like them.
My physical condition is much like yours, with similar restrictions in position and movement. I use a chair blind on my back patio with a thick cushion to raise my seating position. Regular feeder birds come to within 10 feet or less, whether the chair is out all the time or just brought out when needed, less acclimated birds require more stealth and more distance as they react to the movement of the lens, even slight, slow movements, sometimes. When I plan to use the blind, I plan to be in it for at least an hour, usually more than 2, so the birds can forget about my presence or new birds come in. It helps bring in new birds, if there are a number of locals at the feeders/water supply.
Regarding your photos: the position of your blind, the birds' perches or other photo foregrounds and backgrounds need some consideration. Presumably, you have the ability to move these things around to create less cluttered and distracting objects in the images of the birds.
Best of luck.
