I have a pattern for a t-shirt quilt. It says to use non-woven fusible interfacing commonly used for in collars & cuffs. It says to use a light to medium weight. It also says do not use fabric softner.
I will be making one for my nephew with his soccer t-shirts for his graduation next year.

Use the lightest stabilizer you can. I made DD a T shirt quilt and used heavier interfacing and that baby weighs a ton. She loves it though.

as far as quilting - if you can't stitch in the ditch i would do a meandering stitch around the design elements in each tee.

if you look at the above example quilt there's area in the corners and along the sides of each tee block that you would be able to do some free motion stippling.

this way it won't take away from the tee and will actually make the tee design pop out.

THANKS FOR ALL YOUR HELP, GIRLS. WENT TO FABRIC SHOP AND GOT THE LIGHT/MED IRON ON FOR THE T SHIRTS. GD HAS MADE 7 BLOCKS W/IT AND IT IS WORKING GREAT. THEY ARE 14 INCH BLOCKS. THIS WILL BE A FUN PROJECT. :lol: