My mom has this darling high chair. But it has no straps.
When ever we go over there, we've just used a belt to keep the kiddos strapped in.
The problem with that is they slide out the bottom.
So I found a solution...
I measured the high chair and cut out the material to fit over the top.
Then I sewed two really long strips of material that would come from behind the chair, go under my baby's bum, up between his legs and tie in the back.
(Did that make sense? I can draw a diagram if anyone is interested.)
It works perfect! When it's dirty, throw it in the wash.