I have a 26 string harp(from C up to G, 1 octave below middle C, 2½ octaves above middle C) with no levers that I have been playing for 3 months. I am taking lessons and have so far found plenty of music but none of the exercise books I have found are really small non-lever harp friendly. I appreciate any suggestions!
This one may suit you: Bedside Lap Harp Compendium by Cindy Blevins. It’s made for 26 strings, all in C (and minor/modes) with no levers. I don’t own it, but I’ve heard it’s good.
I highly recommend some of the collections by Harper Tasche for the small harp: http://www.harpcrossing.com/
Some tunes may require levers but many do not. Ask Harper what he would suggest; he’s a really nice guy!