Think a bit more about that curb idea. Water gets in the smallest entry space, then sits there and rots wood and lets mold grow. You are proposing to put a short wall next to, but not interconnected with, a shower floor. The walls on either side of the proposed curb are not shower walls, but drywall with paint. So if water gets by the curtain, it can trickle down the wall and get in the slit between the wall and curb, or between the curb and shower pan. Disaster.

You can get heavy canvass shower curtains at the Vermont Country Store. You don’t need to wash them weekly.

Consider using a thick clear mildew/mold resistant shower curtain liner hung to hang inside the curb of the shower -- can be used with or without a second curtain for purposes of decor.

Just "drywall" will not be a decision for your shower wall. It may be that you need to hang the thick clear mildew/mold resistant shower curtain liners on all sides of your shower.

A relative was telling me about someone she knew that used metal roofing vertically hung on the wall in lieu of dry wall. It comes in different colors.

https://www.google.com/search?q=roofing+tin+used+as+shower+wall&tbm=isch&ved=2ahUKEwiN-4us25DvAhWogXIEHShKBlMQ2-cCegQIABAA&oq=roofing+tin+used+as+shower+wall&gs_lcp=CgNpbWcQAzoCCABQh7UBWI_OAWDWzwFoAHAAeACAAYQBiAH9EJIBBDYuMTSYAQCgAQGqAQtnd3Mtd2l6LWltZ8ABAQ&sclient=img&ei=Qbc9YM3WHaiDytMPqJSZmAU&bih=626&biw=1366&client=firefox-b-1-d#imgrc=_qGi5pzglr9XGM 

@Nancy in Mich- I am not sure why you think the side of the curb will not be supported by the walls- perhaps I should have been more clearer. The curb, I think can be built with brick and cement. I suppose it is possible to seal any gaps between the curb and shower pan using silicone caulk. Thoughts?

@suezbell- WOW, the metal walls are something I have never imagined.

They make extra long shower curtains that will go inside the curb to the bottom of the pan. I use a cloth one like they have in hotels and I only wash it maybe once a month with a load of whites and bleach. No mildew on it ever.

We have a stall with a 4" curb. We use a nylon type cloth curtain, like used at hotels. No mold ever. We wash every few months. The secret, for us, is that we always pull the curtain shut after showering to eliminate folds that will trap moisture.

A shower curtain without a hem will develop less mold, but a fabric one is easier to wash every month. I'd prefer the fabric curtain, like in hotels.

Thanks folks. I think we will survive with a heavy curtain.

What’s in a Name, I envisioned your shower curb addition to be outside of your shower pan, built on the floor in front of it. The shower walls end where the pan ends, right? That is why I was seeing drywall walls on either end of the curb. Are you proposing to build it on top of the pan, itself?

You do know that concrete and cement are not waterproof? Water seeps in and sinks down and must drain out, or it sits and smells. Brick layers put weep holes along the bottom of walls.

How will a fiberglass pan react to having bricks and concrete on top of it, and flimsy walls to the grinding of the curb against it as the house flexes with the seasons? It sounds like a mess, to me.