Check out our Golden Nuggets section for much more about open marriage/polyamory basics. You can design ethical-non-monogamy any way you want, as a swinger, as fully polyamorous (emphasis on the "amor"-- love), or anything in between.
What you may want is to each have a secondary, where your lives may be less than fully entangled. This is perfectly reasonable and common. Check out this article, on the rights of secondaries (and how the original couple should treat them).
All the articles in Golden Nuggets are great:
Then there are dozens of books, and at least one awesome podcast too. Happy reading! Take your time. Most formerly mono couples who become successful at polyamory take at least a year to research and become fully informed before starting to seek or date others.
My one biggest caution is not to expect to "share a third." This is usually a recipe for disaster, and best left to fantasy. It's almost impossible to balance feelings in a triad.