Front of house: You could exchange the window to a door in the mud room/laundry, remove the small wall/doorway. You may have room for a dog bathing area and continue the storage. Place the laundry room at the opposite end near the hallway, which will more convenient as well. Keep the door into the garage, as it's handy. By making an entrance here, when you are coming home everyday, you'll be using this entrance vs walking right into your living room.

At back of house: Add a door to the outside from the den and since you wouldn't need a full blown mud room (most storage would be at the front of the house as it would be used more frequently) just add some hooks and a large mat and continue the décor in the office/den to compliment. You could add a barn door at the location of the door into the washroom, so you shorten the hallway and can incorporate the extra space for den/office use. You could add a desk along the wall next to garage, a couch on the wall on the right and your storage next to the back door.

I think two mudrooms would drive me crazy. My boots/coat would always be in the wrong one and then I'd have to carry them through the house (dropping crud all the way). is it really that impractical to just enter the house through the garage when it's just you and family during the winter?

Thank you, Maureen! Great idea to incorporate the mudroom into the office/den! You're right that some hooks and baskets/mat would be plenty to get the job done. Plus, I like the idea of having a barn door to the bathroom from the office, as it functions as an en-suite if guests are to stay over. Thank you so much!

Leila, that's a good point re: boots and coats being in the wrong mudroom! I hadn't thought of that.

I can't see a way to add (or replace) the mudroom anywhere else practical. I would just get my spouse and kids to always enter through the side garage door. You could put a keypad entry on it for ease of use. Moving it to the office would save only a few steps.

Thank you, Leila!

A minor bump out behind the den and bathroom does it. OR, move the den to the front of it's area leaving a small mud room at the back part.