It’s always best to go as big as you possibly can.
The minimum size for two females is 120x60cm. This is the welfare minimum but with a recommended size of 150x60cm for two females.
For three females you would need a welfare minimum of 150x60cm but 180x60cm being recommended.
For two boars, you need a minimum of 150x60cm but 180x60cm is recommended. I would urge you, if you were to get two boars, to always go bigger than the minimum as lack of space can cause big problems for a boar pair.
Therefore, if you are set on a ferplast or commercial style cage, then get the 160 (which is the biggest size commercial cage available) and stick with having two sows.
A c&c cage is a very good option as they can be made as big and any shape as needed.
C&c cage size for
two sows is 2x4 (approx 150x77cm)
three sows is a 2x5 (approx 180x77cm)
two boars is a 2x5
This is our cage size guide and other cage guides
Cage Size Guide
Member Gallery: C&C cages/homemade cages
Member Gallery: Commercial Cages