Tiny, the word you put on the second line has to have some connection to the word you used as a rhyme in the line above. It is not supposed to rhyme with anything, it's the meaning that's important.
Why don't you try this? Leave Jump - Thump, as they are all right. But for your second line think of another word that Thump makes you think of. Not a rhyming word, just a word with a "thump" meaning.
(Don't just "think of," type it as your second line.)