I have several of the smaller IM AIO's, which tank do you have?
I personally do not like filter socks, I don't care for cleaning them. For this reason, I don't use them. I have a three-tier media tower in my IM 15, for example, and instead of a filter sock I run the tower with a pinch of Poly-Fil in the first (top) section for mechanical media. Poly-fil is exactly the same as aquarium filter floss, but much cheaper since there isn't a picture of a fish on the bag. Poly-Fil can be found in the craft section of your local Mega-Lo-Mart, or craft stores like Michael's (it's typically used to stuff pillows and kid's toys). It's so cheap that I simply pull it every few days to a week, pitch it, and replace it. No socks to clean
I then run whatever chemical media in the middle section, and in the very bottom section I tend to place some small plastic bioballs or plastic pot scrubbies I get cheap from my local dollar store for biomedia:
Please know that I don't believe that a reef tank needs "extra" biomedia. Your rock and sand and other surfaces all grow beneficial bacteria, and, according to some experts, using too much biomedia can be a negative.
However, I personally suggest that everyone runs just a little plastic biomedia in their system that can be pulled and used to immediately start an emergency tank or hospital tank. Many people are caught off guard when a disease or emergency issue happens. I suggest being prepared by at least having some mature biomedia on hand. I suggest plastic specifically because plastic doesn't interact with medications, like ceramic media can.
Then, you've got your whole refugium section and return section open for more gear like your skimmer
I hope this helps and good luck!