My sister has scoliosis and really can't do much either. And honestly, I don't have much advice there. She will join me on walks sometimes but I know that still that is even a struggle for her. However, she does enjoy it! Like I said, I don't have much advice on this because she isn't really a health nut of any kind. Exercise is a no go for her, and I don't know if that is just the way that she lives or if that has to do with the discomfort she has felt from it all of her life because of her scoliosis.
As for the pop, here is my experience. Once switching to water ONLY, I haven't wanted pop. Even when it's around. I just don't prefer it anymore. So, you could try that out and see if it works for you. Otherwise I would do either diet pop or flavored seltzer water. You can also work down from pop > diet pop > seltzer water and see if you can eventually get to water then from there. Don't forget about tea! It's another good one! And since it's hot, you can sip on it for a while instead of chugging it down.
As for boxed meals - much as I love food, I don't do fresh food very often, besides when I decide to make a salad or sub sandwich. I pretty much only eat boxed foods. It works for me because I'm counting calories, so as long as I stay under my goal, it doesn't really matter whether it came from a box or the produce aisle. NOW, that is only for weight loss. If you're looking to incorporate healthy eating rather that cutting calories, you probably want to look into meal planning. Get on Pinterest, there are hundreds, probably thousands, of easy healthy meals. You can do freezer meals so you don't lose the convenience of easy cooking/low prep, you can do crockpot meals, you can just do regular ol' prep and cook right now meals. It sounds like meal planning will work for you because you don't have to worry about what's the easiest to grab and make fast from your pantry, food is already planned out a week in advance.
Hopefully these suggestions can actually apply to you in someway and help. I remember starting in February, I wrote out a thread about how working retail and trying to lose weight is impossible. And back then I really felt like I was backed in a corner and wouldn't be able to do it. But I've lost 15 pounds since and I have a full fledged system at this point that is working for me, despite my initial fears. You just gotta try things until you find the system that works for YOU. It might not be immediate - it could take some trial and error - but you'll figure it out. The most important thing is to not give up on it when the first thing you try doesn't work.
Best of luck to you.