When I first use a snaffle, I like to tie the top of it to the noseband, I use a strap through the rings; so that after so much "pull" you start to pull the noseband, which is similar to the bosal. It looked funny and I was once told by a cowboy that the bit strap was supposed to go UNDER the nose, not over it!
But it worked for me. (I switched to the snaffle because I'm not good enough to stick with a bosal: I can't turn very well with it. But make sure you check the teeth for sharp edges, and the height of the palate. I had one horse much preferred a simple straight bit, hated the snaffle. So I used a no-port pelham I had, just 1 rein, no chain.)