From what you’ve described, I’d say regular apple seedlings would be ideal. A stool bed isn’t necessary. When planting seedlings (as opposed to using clonal rootstock), it truly is a mixed bag - you never know exactly what genetic traits the seeds will possess, but the dominant traits of seedling rootstock usually produce a vigorous, widely adaptable, hardy tree which takes a fairly long time to produce fruit (about 7 or more years). Since those traits are dominant, seeds from any regular apple (malus domestica) should do fine. I save seeds from apples and put them in a paper sack. In about December or January, I put the seeds in a zip-loc bag with moist peat moss and put them in the refrigerator for about three months. This process, called cold stratification, simulates winter conditions and is necessary in order for the seeds to germinate. After that, I plant them in the spring. They make great rootstock the following spring. Antanovka and Bud 118 are indeed super-hardy, but in zone 4b, I don’t think you’d have any problem with seedling rootstock. Plus growing your own seedlings gives you more control over your rootstock and avoids the shipping problems that your original post addressed.
I have a small apple cider press and I always end up with lots of seeds in the fall. If you’d like some, I’d be happy to send you some this fall. Just shoot me a reminder, because I’m sure I won’t remember 6 months from now.