Mattress topper for 20month old

[RubyRed401]

Hello!
I’ve heard good things about mattress toppers for little ones. I have a 20month old , not great sleeper and was wondering if it would help?
Has anyone had any success with them?
If so, any recommendations on which ones to buy?
Many thanks

Sorry I’ve put it in the wrong section but not sure how to
Move it!

Not sure when safe sleep guidelines change from saying should be a firm mattress? Sorry no recommendations!