Welcome Mary!
I think the key thing to maintainiing what you lose on the program is that you never stop doing the program. You just incorporate it into your daily routine until it is the routine. In the process, you eat healthier and make better choices, and that's what keeps you in the right direction.
I started off close to what you are at, and know how its like to think that the goal weight seems soooooooooooooo far away. Honestly, I can't remember the last time I was my goal weight... probably first year of High School if I was lucky!
Many years ago, nonetheless.
So don't look at the big, seemingly unsurmountable number. Look at the short term goals, which is to eat on program, exercise if you can, and to look towards losing that first 10%. That's what is attainable, and will make your doctor happy and you'll feel a lot better. Then you concentrate on the next 10%, and go from there. Just taking it one step at a time.
That's an interesting comment about the yogurt. It will be interesting to see how it works out!