Assuming you are for real and not a part of the recent influx of trolling, I would say that football impact shorts will work fine as long as they are the newer lower profile type. I actually used an old tailbone pad that I found laying around from my playing days until I bought some actual impact shorts designed for snowsports. It worked well enough but not as good as the newer shorts. Really, just using a tailbone pad will go a long way to helping you as a noob.
If you are a troll, then fuck off. And to the mods, this is what happens when you let obvious trolls run rampant in the forum. People like me who just want to help become gun shy and start telling innocent people to fuck off when they didn't deserve it.
Drinking the Kool-Aid:
NS Heritage 166X