Our therapist had suggested an open marriage to get our needs met

I find this so weird but I don't know the backstory. Opening up to get needs met is rarely a good idea (with few exceptions). I hope your therapist has experience with it and can give good advice.

I would recommend that you observe and read up on the differences between casual non-monogamy and polyamory with swinging as an option as well. Visit the different subreddits and ask questions. Polyamory is a very resource-intensive and consuming relationship type compared to casual non-mono and swinging. The differences are so big that two people in a relationship where one prefers casual/ swinging and the other prefers poly are often incompatible. It can almost be likened to a mono-poly relationship.