Lots of info is not needed until a layout is decided on.

Is this new construction or a remodel?

With a remodel, you should try to take advantage of the current location for plumbing & vents

Where do you want the door to swing when you enter the room?

It's possible you're just trying to jamb too much into this space.

If a remodel, it's super expensive to go with a curb-less shower. I'm doing a bath reno right now and in spite of my contractor trying, the only way I can get a curb-less shower is to raise the bathroom floor which means you'd have to step up into the bathroom which negates the advantage of an accessible bathroom for mobility impairment. You can drop down but depending on what's under it, can get very costly.

If you don't want moisture in the rest of the bathroom, you may want to rethink the wet room concept.

Check the code for a chandelier over the tub.

The location for the sun tunnel will in some way be guided by what's above the bathroom and how the plumbing vents. A flexible tunnel provides more options, but there are always limitations. I'm sure you have lots of options, just narrow down what is possible and then decide.

If you're in the US, placement of grab bars and handles have ADA guidance. Check that out.

If a renovation, moving the toilet and any other plumbing adds a lot to the cost.

Thanks for both of your replies. This is a remodel. The existing toilet is actually in the top left corner; shower along the left wall below the toilet; and the sink is in the top right. The new bathroom will not be in the existing bathroom.

Thankfully, all the main water lines are directly below us in the basement which is easily accessible due to the drop ceilings.
I should add that my partners dad is a plumber so we’d like to make the project relatively easy for him, but are not too worried about costs. I will ask him whether it is feasible to have a curbless shower.

Existing hvac is currently next to the existing window.

Given that it is a master ensuite and that privacy is not as much of a concern, we are going with pocket doors to save space.

This is the only bathroom on the main floor at the moment. There’s future plans of adding a small second bathroom with only a shower., the existing bathroom is 9”6x6. We are hoping to separately fit a shower and a tub.

Re: wet room, I essentially only want the bath and shower area to be wet. Perhaps I’ll put the vanity and toilet on the same side to avoid getting those areas wet. I could also just rethink the whole wet room thing though.

Personally if the toilet is located on the left wall at the top of your drawing, I would try as much as possible to leave it as is. With the toilet being just by the entrance, I would find it uncomfortable to be using the toilet when partner is entering the bathroom (unless you lock the door). At least if the toilet is concealed it is not as bad.

Does your current bathroom has a shower but no tub and you want to had one in the space you have?

The title of your post says that the bathroom is 12'6" x 9'0" but you are saying that your current bathroom is 9'6" x 6'0". Are you extending your current bathroom and also adding a new bathroom somewhere else in the house?

Hi Suzanne, thanks for the insight. The hvac will definitely be moved.

To answer your questions, the existing bathroom is being moved the next room over into a bigger space to make it a master ensuite. Down the line, we will add a small second full bath. We currently also have a powder room on the same floor.

The current bath has a tub shower combo, but we want them to be separate fixtures. I’ve actually started another floor plan that might give more privacy re: toilet.