I am finding the sideswiper a hard instrument to master. i was hoping it would be easy to just translate my straight key fist to a side-swiper fist, but alas that was a naive hope on my part 
The sideswiper is really quite different in feel and operation from a straight key. Developing a rhythm with side to side movement is really more like using a bug. I mostly use a bug.
I enjoy using a good straight key, like a Swedish Pump design. I'm comfortable with such a key at speeds up to where a bug works well, 18 wpm or so. I think the cootie is easier to use than a straight key at speeds of about 16 wpm to 20 or 22 wpm.
I found that using the cootie a few minutes at a time once a day over two weeks taught me to send acceptably with it. I did find that I was sending dits too fast for my overall speed so I concentrated on keeping to a good-sounding rhythm.
It may be helpful to look at some youtube videos of people sending with cooties. I don't think it particularly matters what kind
of key or paddle you use, any side-movement key can produce good code as a sideswiper. It may be critical to really open up the contact gaps when sideswiping. I don't think the usual microscopic paddle settings which most people use are appropriate for sideswipery.
I have a few single lever paddles which I use as sideswipers. I also have a hacksaw blade cootie. I have a double-lever paddle which I can also use for sideswiping. The key matters a lot less than having a sense of rhythm and setting up the key appropriately.
The nice thing about a hacksaw blade cootie, or some more complicated designs that work similarly, is that the contact "landings" are soft, so that the feel is like that of a Swedish Pump key. The soft landing contact setup also makes the key work much more quietly. Using a hard landing paddle as a sideswiper can be very noisy.