Check out my overview page:
sp00n.net
Measure your current saddle height from the top end of your seat tube to the middle of the saddle rails, and then also measure the available space inside your seat tube. Preferably with a fixed seat tube, but a measuring tape would also work (if you manage to hit the blocking bolts).
Then enter the minimum travel you want in the first filter box, the saddle height in the second, the available space in the third, and also tick the "activator" checkbox as well. You should then see a list of the dropper seatposts that
should still fit in your frame (no guarantees though!).
Grinding down the bolts gives you another 2-
3cm of available space inside the seat tube.