Must admit on small seam I tend to use my thumb nail. After some projects it has a centre dip where I have worn it down. It is very cheap. Ps my nails are very strong these days

DH made me 2 out of oak followed from a picture in book. They work well for small seams. He slanted the ends so that they lay flat on the seam. One is wider than the other,

Along with all of these suggestions, try pressing on a pressing ham and it'll help your seams open up better. It also helps that if you use heat you can use the roller or clapboard right after you apply the heat and it locks the seams open more; or closed if that's what you want.