I got a 4 inch Bounty Hunter coil with the Whites connector for it (see link below to find out where). These run at the same frequency as the Whites 5900's and 6000's and work fine. I use it on my Whites 5900 DI Pro sl.
How small do you want to go, and what kind of environment?
The 350 sniper is pretty tiny, and works very well in very trashy environments.
The Blue Max 4x6 shooter is quite narrow, and will work better in heavily mineralized environments.
The Bullseye 5.3 is a little over half as big as your stock 950 coil. It won't get nearly the depth, but is a good compromise between target separation and ground coverage.
Finally, the Royal 800 is just a bit smaller than your stock 950, and will get very nearly the same depth with less weight and a bit smaller footprint.
I used the 800 for quite some time, but prefer the greater coverage and depth of the 950. This also means the difference between the 950 and the 5.3 is enough to qualify the 5.3 as a small coil. It is a good choice for parks and handles pretty well in trash. The tiny coils just give up too much depth to be used as a main coil, IMHO.