More space is better. I started out with 5’x8′ farrowing pens with a 5’x8′ piglet creep at the end and my girls got stir crazy after a day or so. I’ve since expanded them to 12’x14′ and the sows are much happier and we’re losing fewer piglets since they have more room to run around in and get out of the way when the sows lay down.
One thing I will be adding one of these days are “piglet rails”. Stand off rails that the piglets can go under when the sow lays down and she’s too close to the wall, allows them that extra space to get out of the way.