You also need a wall supply. Depending on the handshower you choose, you may also need a separate check valve. I was told in a showroom, that Moen puts their check valves in their handheld shower, so the wall supply doesn't have one. But, you can buy one. Hansgrohe, however, doesn't put one in their handshower, and you can buy a wall supply with or without the check valve (I believe), so you need to make sure you buy the right one. It is okay to have more than one check valve, but you want to make sure you have one.

One generic name for what you're talking about is "handheld shower". Have you taken a look at the big box stores (L's or HD)? They have displays which probably have what you want. Yes, there are those like yours with brackets that attach to the shower arm (the pipe sticking out where you normally attach a shower head.

Sounds like you need a item called a wingits. It is made for attaching grab bars without studs behind them Here is a link that might be useful: wingits

I hate the feel of hair on my body -- gives me duck bumps! -- so I wash my hair in my extra large MBR sink. I *could* easily wash it using the hand-held Grohe that can be positioned 'wherever' on its vertical pole. There's *plenty* of water pressure through this. The house is 14 now; no slipping, sliding, or other problems with the hand-held. (We had an old Speakman head in our condo until recent remodeling. Minimal difference.) OT: One of my favorite things in this house is the recirculator on the hot water line. This provides hot water in seconds at every hot water tap in the house. Now that I think of it, even with that fast delivery, I push the hand-held shower spray away from me for those few seconds and flip it back when the water is hot. We should start a thread on how long you spend IN the shower, after all the debate about the water delivery system!