design shower/tub layout in master bathroom

We want to remodel our master bathroom. Attached is the original architectural plan of our bathroom and photos of our current bathroom. The current shower is too narrow. The wall between the shower and the tub has the shower faucet controls in it. It is actually 8" wide, not 4" wide as shown in the architectural plan. If we move the faucet controls to the opposite wall, we could remove the 8” wall and put a glass partition between the shower and the tub and make the shower wider. I believe between 40" and 45" width would be good for the shower. Our current bathtub is 24" deep, but it is sunken 16" below the floor, so it sticks up 8" above the floor, and the top edge of the tub is flush with a tiled deck that we sit on. The deck is about 12" wide which is good because we can sit on it when we wash the grandkids in the tub. We now want a rectangular, slightly shallower tub -- maybe 20" deep x 5' long, and we want a step into the tub at 10 of 12" high, so the tub would be just a little higher than the step. So, the bottom of the tub would still be sunken below floor grade. Attached is a photo of our idea, more or less, except we want the tub sunken the way our current one is. Another idea is to use a trapezoidal tub... attached is a photo. It is by Duravit. The glass on the shower would go to the ceiling. We would have a mirror on the wall behind the tub. To the right of the tub is a glass window. One idea I had was, that depending on the angle of the tub, maybe the entrance to the shower could be on the side of the shower instead of the front. We are hoping to have 3d rendering of this after we decide on the exact tub and get the exact dimensions and layout of the shower and tub. Also attached are some photos of ideas we like, and here's a link to a look we like: [login to view URL]