That could be a good solution, a fisher type bowlmate made of a hollow shuttering ply box type structure filled with ballast, with a removable or replaceable cutting block. Thats what I used for my lathe bench (6 bags of 20mm gravel) and it has greatly reduced, in fact all but eliminated unwanted vibrations. Any workholder or bench that is too light and/or flimsy is a waste of time
I have made one of those for hollowing bowls. Believe me the twin wedge (folding wedges) system is the simplest, time honoured and best method to quickly hold the work secure, and release it just as quick when you need to. I get nervous when theres taught straps and come alongs etc...and sharp blades swinging about. What really works for that horizontal clogmakers design is that you simply turn your whole body 180 and you are instantly working the other way, no need to fanny about repositioning the wood. Something like that set at an angle against a wall would be great. The only downside I found was a bit of back strain. I prefer to sit to work LOL being a bit older than many
The 5th picture looks like the work isnt fixed. From what you said, I'd be looking at building up that style from a vertical 5 x 5 to lean against a wall, with a tee piece on the bottom end to rest on the floor to make it stable, morticed and tennoned together preferably, at the very least half lapped. And have a pair of blocks fastened on top of the upright 5 x 5 with a suitable gap between them to give enough space for the work and a pair of folding wedges, or set in sturdy oak or ash pegs to rest the work piece on. pegs are versatile, simple and easy to modify as and when you need to. Here is a video that shows my chopping block and how I use pegs to support the work on my chopping block, gives you the idea even though this is a big piece of willow (end grain willow grips the work really well without it slipping)
https://youtu.be/RiTJY9k0hko