Standard staterooms (Cat 11 & 12) are pretty much the same size as Deluxe staterooms (Cat 10 thru 5). The only real difference is the split bath which elongates your entry hallway and increases your storage space.
The main part of the stateroom doesn't really get bigger until you move up to a Cat 4 stateroom where the length of the room is extended to may space for the murphy bed by the verandah.
You'll still have to decide if you can handle an inside stateroom vs a stateroom with window (porthole) or verandah. If you can stand to be in a windowless bedroom, then you shouldn't have a problem with an inside stateroom onboard. The size of the staterooms is equal to a queen size bed with 2 feet a clearance on three size, and multiply that space by 2 (I'm not sure, but the side of the stateroom with the couch/coffe table/tv feels to be the same size as the "bedroom" half of the room).
We've always done a Cat6 except for once we took a last-minute cruise when they had a special trying to fill up Cat 11 rooms during off-season. The size of the room didn't really feel any smaller, but we instantly noticed the decreased storage space (both in the cabin AND the bathrooms). Make sure you take along an over-the-door shoe holder for extra storage.
I'm going to make a guess that the size of the "main" part of the stateroom (based on the furniture and the way it's laid out) is about 9 feet wide and about 16 feet deep. Seems to fit in with the quoted square footage (184 for standard which is about equal to 9x20 when you include the space for the bathroom, and 214 for deluxe which is about equal to 9x24 (four more feet for the split bath)).
BTW, to give you an idea how similar the rooms are, I noticed that
DCL's own web site uses the same "movie" (those 360 degree views) for both Deluxe and Standard inside staterooms. You don't really see a difference until you look at the floor plans. But there again, you will see that the main portion of the room is the same size for all these cabins