I also want to see you progress on this!
There are many options out there, if you do a search on "memory quilts from shirts" you will get a lot of pictures and links back to this site!
I count shirts as 1 FQ -- the backs usually have a piece about that size in very good condition. There are the front and sleeves and pockets, too.
Blue Chambray or Oxford fabrics (both shirting types) are easy to buy as yardage. Or, if you need to fill out what you have, the thrift stores are full of more shirts, particularly basic tones. Around here, all the different stores (Goodwill, Salvation Army, Value Village) have a colored tag model where basically things only stay around for a month, and then go on a super sale price. The stores also have different days for things like Seniors or other discounts.