I spalled up a couple of pieces of the S.A flint as an exercise and used a good sized rounded river stone as a hammer. So as to be a early era exercise and despite my lack of skill got a few flints made.
Put the stone on my leg with a heavy cloth as most of the videos about show. One day will get a large piece of leather which would be better.
Have the same bopper as yours and it is a really excellent tool.
those boppers are a magnificent tool, expensive (mine cost something like $80 posted) but it is exactly the right tool for what I am doing, heavy spalling and bi-face spalling. Plus they are so well made they will last a good long time. I know mine has held up well for a while now and will do so for a long time still.
As far as a leg piece, yeah just a piece of leather seems to be the preferred way to go. A cut glove and glasses are a must IMHO, just not worth the injury to the hand or eyes.
Apart from the bopper also bought the tool with a copper spike for edge knapping. This tool comes in handy for a quick touchup of an edge. Along with a block of coarse material for tidying up edges. Must admit have not used the block much.
Yes eye protection is essential as tiny shards can fly everywhere.