https://m.ikea.com/us/en/catalog/products/art/80240440/ II've used these from ikea for a few months now with no issues...

We put 3 in our powder room shower just off the entry from the pool. Ideally, this should be preplanned so you can drill into wood and not have to use anchors. But you can do either method. The contractor used a special drill bit. Drilled carefully so not to crack the tile. Silicone around the hooks. We also have one in the main shower for loofas and towels. We love them. They match the towel bars. Consider that there are much larger holes in the tile where the faucet and other shower fixtures come out of the wall. Only silicone protecting those areas.

Our other bath I mentioned.

Completely different idea: Are you old enough to remember that hotels used to have "retractable clotheslines" over the tubs? They were very small -- about something the size of a metal tape measure -- and were installed just above the tile -- you could pull a little tab /pull it to a "catch" on the opposite side of the tub. They were convenient.

There are thumb hooks and cone hooks that are installed before tiling.

https://www.flooringsupplyshop.com/tileware-promessa-thumb-hook-contemporary-2334.html

https://www.flooringsupplyshop.com/tileware-promessa-duo-cone-hook-traditional-2327.html

3M Command has stick on hooks made especially for the bath. https://www.command.com/3M/en_US/command/products/~/Command-Products/Bath/?N=5584706+5924736+3294529207+3294857497&rt=r3

I use Bobrick hooks in my bathroom for towels and robes. If you put them in the shower you would put silicone on the screw holes and caulk around the top edges. I use the B-211

http://www.bobrick.com/washroomaccessories/Pages/Products.aspx?Category%3DHooks%2FShelves%2FCustodial+Accessories

Consider installing a good-looking grab bar near the entrance to the shower. I have one that acts as a towel bar for the bath mat. It has knobs on the ends where I hang wet stuff to dry. Works great and doesn't look therapeutic. Plus, you never know when life might take you in a new direction and you'll be thankful for the added stability.

@pamal66: Those tileware hooks are really cool. Interesting install.

I have had command hooks in my shower for 9 yrs, and they work very well. Easy to clean too.

We have one of these Over the glass hook that I was going to install turned inward for shower scrunchies but our glass wall turned out to be too tall for it to work for short me. So we turned it outward and use it to hold the bath mat. They also have a style that is installed through the glass. May not work for you but I thought I'd mention them as I had not seen them before our shower glass company showed them to us.

JM, do you have a link for the company of the glass hooks? I wonder if they would be good for the glass shelves inside niches.

I just found the link on the top of the page of the picture you included.

http://www.distinctiveglass.com/products/hardware

pamal66, I don't think they would work on shelves, they need to be installed in/on a thick vertical piece of glass. If installed on a horizontal surface I think they'd be to shallow to function well as a hook. The local glass place that carries them is Distinctive Glass.