Hey there!
What I’m getting from your post is that, when you try to do a pole sit, you find that it either hurts quite a lot, or you slide down.
Unfortunately, pain is a part of pole dancing, and for many of us the pole sit is our first introduction to the pain of gripping the pole in a sensitive place.
The issue of sliding, however, can be corrected in a number of ways! Certain leg or hip positions, such as leaning one hip down toward the ground, and putting your feet toward the opposite direction, can help to create a “lock” so that you can get used to the hold.
For something like the crucifix, which you mentioned, it can also be somewhat painful, but the hold itself is a bit different. You’re holding a lot more with your lower legs, such as your shin and your calf. This move can actually be used as an advancement from a squat, if you so choose, due to the difference in hold. However, you have to really concentrate on squeezing hard with your hold.
Things like a warm pole, and a warm (but not sweaty) body can also help with your staying on the pole, of course.
Hope this helps!