Here is the problem I am seeing. You wouldn't be able to find a job until you moved, as I know this from experience. You have to prove you can support yourself on savings for the visa. Now, I have worries here in what you said:
"Jobs here, in my area with our experence do not pay enough or do not have good benefits"
The world is in a credit crunch, and the cost of living in the UK, in most areas, is incred. high, higher than Texas. You have to think that if you were to move, you'd have to be unemployed while looking for work in an incred. competitive job market. There are too many people here in too small a space, and even the most basic of jobs have no less than ten other people competing for the same role. So finding a job, and more importantly, a job that will be able to support two people in a country where costs of everything are well inflated will be a challenge.
Obviously, private health care is not going to be an option what with the pre-existing conditions. However, actively seeking employment with a company that has a good package might be an option.
Also, there are things you can do now. You said you are boarderline diabetic, but youre not yet. So research on the net how to control your condition through diet. Dont let it become full blown diabetes, dont wait until you need medicine and expensive doctor visits. Get it under control now with low sugar and low sodium diets.
Secondly, and i dunno how you may take this, but have you ever talked about maybe just giving up the leg with the infection? If you're in this situation where its an ongoing condition, costing alot of money, disabling your wife... is having a symetrical body really worth all the other things? If it were me, and this is just my opinion, I've give up the leg in hopes of a better, non afflicted life.
good luck in whatever you decide. But in my opinion, you'd be better working your ass off to improve your situation in the US, rather than moving halfway across the world. Work two jobs if you have to.