If you want to do mutations such as what is in Metamorphosis Alpha, I would get Strontium Dog, which is also mon 1e. I have done something similar, except that the generation ship had arrived.

Get hold of a copy of [Metamorphosis Alpha](https://en.wikipedia.org/wiki/Metamorphosis_Alpha)

You can pick it up on ebay for pennies

Few thousand. Maybe as many as ten thousand, but I'm thinking more like 4 or 5.

How many years does the setting take place after the ship is launched?

One of my favorite tropes in sci-fi is the lost generation ship where the inhabitants don't know they're on a ship. I'd like to start a campaign on one, in Mongoose 1e. I have the book that has the barbarian careers in it, but are there any other resources that I might want to look into? 

Lost Generation Ship Start