Miniature peach tree suggestions for Zone 5
Most miniature peach trees are small due to the rootstock the variety is budded on. Most of the naturally dwarf varieties are not very hardy. The catalogs generally do not say what rootstock are used. Common dwarfing rootstocks used by better nurseries are Pumiselect and Krymsk 1, which are generally hardy enough for zone 5.
Avoid sites down in a hollow and use sites with soil that is relatively well drained.
Varietal choice is even more important for hardiness. Avoid varieties with low chill ratings (look for chill hours of at least 700 hr, higher is better. Varieties with high chill hrs bloom later). Some of the tougher peach varieties are Contender, Harcrest, Redhaven, Starfire. Reliance is rated as hardy, but the flavor is so-so, Loring, Redskin, and Canadian Harmony are only moderately hardy. Cummins Nursery in New York generally has peach trees / rootstock combos available that are relatively hardy. I would concentration on finding trees with cold hardiness rather than disease and insect resistance as the latter can be controlled with sprays.