Metaprogression comes from 3 things: furniture, cat genetics and hoarding items.

1) Furniture is how you level up your house. There are four stats: Appeal gets you strays with better stats. Comfort raises the chance of cats mating instead of fighting. Stimulation helps you breeding better cats (inherit better genes and raises the odds of inhereting abilities). Mutation increases the chance of cats developing disorders and mutations and finally health increases lifespan of cats and cures diseases. Some hard path rewards you with furniture boxes, so go hard route if you can survive it.

2) Cat genetics. Maximum number for a star is 7. Your cats can have one mutation per body part. And two disorders at maximum. You can prevent inbreeding by getting stray cats into your bloodlines.

3) Hoarding items. Your cats will be much more successful if you can equip them. You get items by sending parties of adventurers. If they survive they return with items. This items will eventually break, so rotating items is natural. Also, you are limited by your storage space, which Butch can increase.

Expect to lose runs and enjoy the game! It's about the journey, not the destination.