I'm guessing that your question has gone unanswered because of two reasons. One might be that the use of walking iris as a houseplant might not be familiar to most of us.

The second reason is that the fern will crowd out anything that it co-habitates with. It's not a good idea to attempt growing them together.

Thanks for the advice. I know walking irises are generally outdoor plants, but in my zone that's not much of an option, so it's nice that they do work as houseplants. Thanks for the confirmation about the Boston fern, I suspected that might be the case, but really I didn't have enough experience with them to sure.

Good to know!

Maidenhair Ferns (Adiantum sp.) might be a better option. They do well indoors and wouldn't dominate the pot. There's a lot of species/varieties to choose from

Good to know, I've had one in the past but had a hard time keeping it watered enough. But in a big self watering pot, it would be easier, I'll have to give it a try!