My budgie when I was hand raising him his first few days of life would move about a lot like that. Sat up and wobble until falling over. It’s normal, they’re just trying to figure the world and themselves out.
If you make the bra, put it on while the crop is empty so you don’t push food up out of the mouth and cause the chick to aspirate. It’s pretty hard to squish the chick with the self adhesive tape, but I did notice that the bandage would stick to their feathers a bit
I just used warm water and a q-tip to nicely pull off any spots that their feathers were stuck to, but with a cockatiel I’d probably use a piece of cloth or something under it. You’ll need to make a new bra every day since the chick should be growing fast.
The biggest mistake I made when I was dealing with my malnourished chick was feeding too slow. It caused air in the crop which caused malnourishment as well as an overstretched crop, yeast, etc etc. You do really have to put the food in fast, watch how birds feed their young- they only push food in once or twice in total! If you can’t do it with the syringe you have, you should try spoon feeding. When I started spoon feeding (I had waited until the chicks eyes were open but I have seen people do it before) my budgie didn’t get air in his crop anymore.
And now since the crop has flushed properly, feed the formula at the proper thickness for the age. I think by now the formula should be fairly thick, that’ll help with malnutrition. And feed as much as possible every feeding, don’t let the crop get empty until the overnight break. When Phoenix (the budgie I handraised) was really young in this stage I was feeding him every half hour to an hour, with only a 3 hour break in the middle of the night until his crop emptied. It was only like that for about a week, but it saved him from malnutrition.