With mono decks you should consider two critereas:
weather some or the majority of your cards will be stronger in mono (like La Junta)
or you have enough strong cards with various abilities to suit your needs (like Uppers)
In case of pussicats the crucial lower region is not solid enough. They have Brittany, and Wanda for 2*, but in the 3* region a wall is qet to be designed. Till that cats will have to team up with men.
Funny Story: Switching over to mono Rescue, and so far could only afford 5 Rescue cards (after getting Glosh). Kept 3 Pussycats in for now til I could get more, and I'm actually doing pretty decent with a Rescue/Pussycats deck xD I usually get 2 Rescue 2 Pussycats, and Rescue provides the power while Pussycats provides the damage reduction.
Also, I'll look more into Pussycats/Sakrohm and Pussycats/Jungo when I get more money, thanks for the suggestions.