How would you layout/configure a master bath expanded into a unused 10x 12 room that is between the bathroom and master bedroom?

We would like to expand the bathroom to include a walk-in shower and free standing tub and some additional closet space for my spouse’s athletic equip and some linens.

We have a mid-1980s two-story center hall colonial home. Having a dilemma with 2nd floor master bedroom/master bathroom re-configuration.

As it exists, enter the master bedroom sitting area from the hallway, the sitting area leads to the bedroom. The sitting area is a separate room with a wall of closets and it sits between the bedroom and bathroom. The sitting area had been used as an office space and catch all room. With laptops, we do not need this space as an office and would like a larger bathroom.

(We do have a generous walk-in closet over the entire garage.)

We would not want to walk through the bathroom to get to the bedroom, so we would want a wall...realize that would necessitate a long narrow entrance to the bedroom from the hall.

The bedroom itself is a shed dormer and has a slightly lower ceiling than the rest of the second floor....so removing the wall between the bedroom and sitting room would be awkward with different ceiling heights.

Has anyone had to deal with “odd” unused sitting areas? Any suggestions on layout? Can you share how you have handled it? Thanks!