Essentially the only thing a hybrid is is using different strings in the mains and crosses. That's all it is.
There are no rules for hybrids. You can use any string you want in the mains and any string in the crosses.
Usually however people hybrid a certain way for a reason.
Poly mains tend to help generate spin and control. However, since poly is harsh and stiff, people will usually put natural got or multifilament (soft strings) in the crosses to bring back some of the soft feeling.
You could also go the other way, with a soft string in the mains and poly in the crosses. This provides a more feel-oriented, softer stringbed but still gets some added spin from the poly.
And again you can just mix and match whatever combinations you like.
The biggest thing to keep in mind is that the mains of your hybrid will dominate the stringbed. That is, if you have poly in the mains, you'll still feel a fairly stiff stringbed even if you have a soft string in the crosses. And vice versa.
You could generalize this to a ratio that about 70% of your racquet's feel and attributes can be linked to the main strings, and the otehr 30% to the string in the crosses.
If you do have a sensitive wrist, you could maybe try a soft string in the mains like a good multifilament and a poly in the cross to give you some help from poly but still maintain an overall soft feel. It all depends on what you're willing to try with hybrids since the possibilities are seemingly endless.
Also, a thing to keep in mind is with hybrids you can also have different tensions in the mains and crosses. For example, people that use poly have to lower their normal tension by usually around 10%, so they might do a poly in the main with 55 lbs of tension and, say, natural gut in the crosses with 58 lbs of tension (or the other way around..nat gut in mains with 58 and poly in crosses with 55). Try not to go for more than a 5 lb difference though, and you don't necessarily have to have such a difference if you don't want to. Usually the reason is if you have poly somewhere, you have to have it at a lower tension than normal.
That about sums it up. If you need tips on what hybrid combinations to try, I would suggest a poly & nat gut/multi hybrid. Look around for some combinations on that. Some people use natural gut in the mains and a cheap synthetic string like PSGD in the crosses to get more out of their one set of natural gut (cost efficiency at a small expense of having syn gut crosses).
Like I said it all depends on what you're willing to try. From your sig it looks like you have your own stringing machine, so you should be able to try some fun combinations out on your own without worrying about expensive stringing charges
