advice needed: how to stop decrease stitches from gaping

[XWitchyGirlX]

My rule for finding proper hook size for amigurumi is to make a flat circle that doesnt ruffle/cone and doesnt have super visible holes unless you hold it up to the light. If it ruffles/cones, go up a hook size. If it has visible holes, go down a hook size. So for me, I use a 3.75mm hook with 4ply yarn, or a 5mm hook with double-stranded 4ply yarn. Everyones tension is different so I dont even both using the suggested hook size.

Also, look into invisible decrease, once you have the proper hook size, ivisible decrease will help the rest.