Be careful with the back of your hand, though... depending on how you're built, you can do some real and lasting damage to the meta-carpals that way.
If he really likes it all that much, it's probably worth investing in some proper toys for the job... In a flogger, you're looking for lots of dense, soft strands... Suede & soft leather (like doe or elk) are preferred, and latex/rubber strands are quite popular, too. Paddles should be broad and flat, out of rubber or leather.
Paddles are generally better for shorter duration sessions with a higher immediate intensity while floggers are designed more for sessions that will sttart off slow and go for temn, twenty, fourty minutes... Or longer.
There are some nice ones at
babes in toyland, but I'm sure there are an assload (no pun intended) of sites that have more due to specialization. If you want to keep it in the family,
CJ used to sell sex toys. I'mnot sure if she still does, but it'd be worth asking.
If you end up wanting advice on technique, I'd be happy to discuss that, as well. Several of the pets I've owned over the years like to be spanked and flogged, so I've gotten pretty decent at it.