Idk if anyone has mentioned this, but check out any reptile expos in your area. My local expo has a vendor that sells frozen feeders (mice, rats, etc.) Then you don't have to pay the crazy shipping if you are buying smaller quantities, and you can see the size of the feeders in person if you aren't sure what to order. The expo goes on 4x a year here, so you can always stock up on what you need for a couple months before the expo comes to town again, and a lot of those vendors will have cards etc. so you can pre-order exactly what you need and just pick them up at the expo when it comes to town. If your snake outgrows the size you have on hand, just feed multiples or more often until you can get the next size up when the expo is back in town.