Design Board Size Options

Hi! I would love to have different options for design board sizes. Right now, they print really nicely on 8.5X11, but I would also like to have an 11X17 option since the proportions are different. We print our designs as booklets for our clients and an 8.5X11 print is just too small to show them the details. However, when I've tried to have it printed bigger, the resolution isn't high enough to accommodate this without the image being blurry. Thanks!