What breed do you have? A banty may be too small, but there are broody standard fowl, as well. Brahmas, Cochins, Sussex and Orpingtons are the ones that come to my mind, first. Silkies are probably your best bet for broodiness, but they tend to be smaller (between bantam and standard size) and you may end up with some interesting Silkie mixes. No matter which broody breed you add, you'll likely get some mixed peeps, but if they all share nesting boxes, you'll get mostly your main breed. If you don't want to keep mixes, just enroll them in Freezer Camp with the rest of your meat flock.