As others have said, what qualities are you looking for to cross the WW with? A sativa high or an indica stone? Tall, short, fat, or skinny plants? Early or late harvest? I like the idea of a Thai cross, but the seeds for those are hard to come by these days. Far easier would be to find Durban Poison land race seeds. Durban is quite popular and you can probably find regular seeds for them. It is a landrace from South Africa, but the strain originated from Thai genetics. It is a pure mental sativa high, without a body high or stoned couch lock of indica. No paranoia, no weirdness to the high, no rushes. But a good high that you will want more of.
Personally I find WW to be a great high as is, so I would not cross it with anything. It is very popular here and I have grown and sold many clones of that strain. As said above, you would have to find regular (unfeminized) seeds, germinate them and grow and select a male from among them, get it to flower and produce pollen, and then pollinate a WW female with it, and then let the female produce and ripen the seeds to harvest. I have grown many males, and they can be messy as they produce GOBS and GOBS of pollen. Us males are like that… horny as we are.
Then of course you have to grow the resulting seeds, usually a lot of them, as the results of these types of crosses (indicas and sativas) have a wide range of genetics and the results are likely to be highly variable. From those you would select the traits and high that you like, and try to stabilize the plant with those effects over the next several generations. Meaning that you have to grow seeds for a few years to get the desirable results in a stable plant that results in stable seeds. This will of course already have been done by many of the better seed crossers and producers out there. So why re-invent the wheel?
There are a lot of stabilized WW crosses out there already, in seed and clone form, as well as siblings of WW like Black Widow. Many variations to choose from, and you do not have to spend the time to grow males and generate crosses and re-crosses. Just my 2 cents worth… if you really want to cross strains to produce seeds, it is easy enough to do. But the results may or may not be what you want or expect. For these reasons I do not breed to cross widely variable genetics, I in-breed to preserve land race genetics.