You will enjoy having 2 or more stops of Neutral Density. If you have Color Printing filters, you could always add equal parts CMY to make ND.

I personally use a 2-stop ND No. 96 Wratten gelatin filter when making small prints. It's only 2x2, and I simply drop it down inside the lens cone, right on top of the back of the enlarging lens. I would rather have 3 or 4 stops because still I have short exposure times.

If you have a camera-grade ND filter, you could put it in the optical path. I've gathered from random threads the feeling that "filters in front of the enlarging lens are not that bad".

While you're at it... do you have a "voltage regulator"? These units hold the voltage steady despite fluctuations of the incoming line voltage. Shouldn't be too expensive, and it can help rule out exposure variations caused by voltage spikes/drops that can happen between two prints that should look the same.