I tried several different layouts for your bathroom, but given your budget and other constraints, I think that keeping the same basic footprint is your best option. The floor plan attached moves your toilet closer to the entry door and extends the shower to 3x5 feet. I tried placing the shower along the exterior wall, but this would require changing your window to a vinyl window with tempered, safety glass.
Ideally, it is recommended to keep 30" space between the vanity and the shower entry, but 24" is the minimum clearance. In this drawing, I have allowed 30" clearance with a 21" deep, 5-ft long, double-sink vanity. Your linen cabinet can be replaced with open shelves or cabinetry to match the vanity.
Your shower head can be mounted on the exterior wall (the pipe self-drains when the water is turned off), and shower control valves can be mounted on the opposite wall. I added a handheld shower head on the back wall of the shower, but this can go on either of the side walls. I am showing a 32" wide, fixed glass panel with a towel bar on the LHS of the front of the shower, and a curtain for the 28" wide opening on the RHS of the front of the shower.
The wall between the toilet and shower can be a half-wall or full wall (preferable if you plan to replace the curtain with a pivot glass shower door).
I like tile on the wall behind the toilet (especially if you have young sons) -- it can be the same as the shower wall tile or more decorative. The TP holder can be attached to the wall on the exterior of the shower wall or the opposite wall. I have added towel bars, but did not address lighting.
Minimum clearance for the width of the toilet space is 30 inches. The wall separating the toilet and shower may be 6" wide, which will decrease either the length of your shower and/or the toilet space.
Caveat: I am not a designer; I am a computer geek, struggling with re-design of a similar-shaped bathroom.
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floor coretec
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