Choices abound. Trees on M27 are the least vigorous, M9 are somewhat larger and longer lived, both come into fruit in their second year after removing blossom in the first spring. Space at about a metre for M27 and 1.5m for M9. Training to espalier means more time needed and more light for vegetables nearby.
I grow vegetables almost up to the trunks of apple trees and they are good, although slightly lower yielding and smaller in dry summers. The fruit chapter in my Organic Gardening book has more advice on all this.
I would order trees soon as the choice diminishes when nurseries sell out.