Agree, use a razor blade. I use a square double sided Wilkinson Sword, but cut in half so you are not having to hold both blade faces.
Parafilm or Buddy tape makes it much easier to cover the grafting work.
I often use a tomato grafting clip, to hold the graft closed while tying the first tie on the rootstock.
The same methods can be used for tiny chip buds or tiny T buds.