I have a few fwbs for whenever my wife isn't in the mood
I hope you are joking? What happens if she finds out?
I'm good at hiding stuff from her.
You can't expect your wife to do it all the time. Stress kills sex drive. Take that equation out and I'm sure she will be ready to go all the time.
What about my needs?
It is never good to cheat on your partner. Usually people are loyal to their partner in a relationship.