You should be able to keep your resistances roughly in line with your level until they cap at 75 just by picking items with some res implicits, affixes here and there and idols. Eventually you'll actually get a very good chunk from blessings.
It is important to note that capping resists isn't anywhere near as important as it is in other ARPGs of you've played those. You might want to look at health and endurance or ward.