in that case, a good solution is to limit yourself to a handful of notes and stick with those notes across all octaves. for example a common scale is C major, which is just all the white keys on a piano (i think pxtone indicates which notes are white keys somehow...). basically, pick 5-7 notes and only use them.
now with your limited note palette, you could first try devising a "bass line". these are lower and often slower than your melody, but tend to command the direction of your melody. a common pattern for a bass line is 1232. pick three notes from your palette to use for that pattern and try it out. here's what im thinking of visually
also, imagine all 4 notes being the same length
as i said before, your "base's line" can command your melody. by this, i mean that there should be some sort of relationship between what the bass line and melody is doing. in the example below, each time the bass plays a new note, the melody also plays that note (in a different, probably higher, octave) but with some additional taster notes after it
im not sure how interesting the example i made here is, but the idea is that you should make some kind of process like the one ive described here and then do some additional experimentation