I mostly use a 12 inch 70 dur, or triple durometer squeege. For left chest images which I have been doing alot of lately, I use a 6 inch 70 durometer. I keep a 14 inch as well in a triple durometer 75/90/75 for the larger full back prints, but even full backs I usually can use my 12 inch.
I try to use a squeegee that is at least 1" wider on each side of my image to be printed. Therefore, you may want to invest in a few different sizes. Typically a 70 durometer is fine.