I wish you had asked back then too. Sadly the sole has thinned out more as a result of shoes.
First I'd get a barefoot trimmer out and see him before you do anything else. They are the best ones to advise you, we can't see the hooves from here. Boots are SOMETIMES in extreme cases used 23/7 for a few weeks, with soaking and treating to prevent thrush and such for the other 1 hour. However that is horse sthat will not move about, to promote circulation by walking. Your horse is not sounding at all in that way and I agree snow is good for the feet so don't make that jump.
On a side boots can also be used to prevent or treat thrush. Not the soakers, I'm just talking about the riding boots. In the really mucky part of the year here if I see any ickys going on I treat for thrush before putting the boots on. Then the medication stays on the foot for the whole ride, or if I'm not riding that day I toss them in the round pen or small pen for a hour. That way instead of getting the medication back into the mud right off they keep it on the foot, and it works wonders. Even if you don't treat for thrush cleaning the foot off and keeping it out of the mud for the duration of the ride is helpful it seems. I was very concerned about boots in regards to infection but I have turned around on that, I think they are helpful. Of course you have to take care of the boots, hose them out every time and spray them with a disinfectant if the horse has infection, then rince again.
Cinnimon is used to lower blood sugar in horses. We don't know if your horse needs that, again a person that sees them in person could advise you on that. The dose is a teaspoon per 250 lbs once a day.
Pat the newer easyboots stay on really well. I had losts of greif with the old ones, and had moved to making my own pads to help keep them on before pads were cool or even offered by Easycare, but they had the idea on their site from other users who had fit problems. But the new boots with pad just do not come off, even if the buckle pops open. Without pad they can come off some feet that as you said are not shaped as that hoof is. In that case they have the room to twist off. Pads prevent that. Easyboots should never be tight! they do not need to be, and in fact now they don't even have backstraps, and you can get a retro for the ones that do. If you can't close your easyboot with just your thumb it's too tight, and if you need it that tight to stay on you have the wrong size. to have the right size if the pads are new you should need to really push or have the horse step on the boot to first get the foot in. Once the hoof has made an imprint in the pad it should go on without that. It being snug all around, just fitting, is what prevents twisting, so then it stays on with just the front of the boot being closed and the gator.
So with this horse I'd just get a barefoot trimmer out and see what they say for now, before you buy anything or add anything more to his diet. Do take out sugar if it's there, but other than that since he is improving wait till he is assessed in person. Most trimmers have boots with them so they can fit you perfectly too, and that is very important. Trying them on is the best way, and some experience doing it.
Good luck!