N.B.
The cribs today have slats that are really close together. I thought 2 inches or less was the common way, so that baby's can't get their extremities through them. I haven't had a little one in a long long time so I could be wrong.
I don't know what to tell you, sorry, but I know you'll think of something. Have you tried pinterest and searching for baby bed bumper alternatives?
I found a bunch of different options.
Wonder Bumpers from Go Mama Go Designs is a wrap that goes around each pole and it pads it just enough that feet and arms won't fit through.
Olli Ella Bumpettes is another option.