Some of the choices are "lockers", while others are termed a "limited slip differential". Limited slip often has internal clutches, or some other mechanism that makes the locking come in more gradually. It sounds like a selectable locker might be your best choice, but they are usually relatively expensive because you need some way to control them (electrical, vacuum, etc.).
The GM factory locker option was called the G80 GovLock, and it was more for trucks (like ours) than it was for performance cars. It has a locking pawl inside and whenever the rpm difference between the two rear wheels reaches about 200 rpm, the pawl flips out and engages the locking mechanism. The GovLock has a bad reputation because if you spin it up too fast on pavement it will lock too quickly, and then sometimes things start to break inside. Hence the nickname - GovBomb.
Detroit Locker has a great rep, but it's really designed for performance cars that want a very positive locking mechanism. It is a very solid locking mechanism, and may chirp or make various noises when turning sharp around corners. I first heard of them in the 70's when they were an option on Ford Mustang Mach 1, Torino Cobra, etc.
I had a Ford Traction-Lock axle in my Torino, and even that could be a handful on ice. When you spin one wheel (no Traction-Lock) it drags the car rear end around relatively slowly because one wheel is spinning and one is stationary. With Traction-Lok and a lot of engine power it was easy to break both wheels loose very quickly on pavement, and just about as quick for the car to try to completely swap ends. On ice I learned that once it lost traction the rear of the car started a slow swing out to the right and I had to let up on the throttle and try to manage it by steering back the other way.