Honestly, probably about the same lol.
In my springer, I use 55° 4mm rubber that I punched out of a sheet, but anything will do really.
As for the rest of the noise, what barrel, spring, BB, and speed are you using?
If your barrel is too short or your BBs are too light your gun will be a bit loud.
A silencer will only do so much, but I suggest a 32-37mm outer diameter one, no more, no less, as I have found that diameter is about optimal for some strange reason.
For picking one out, just get the coolest looking one to you, and make the filling out of some open cell foam or some Scotch Brite.
For more silencing effect, use the smallest holes in the foam and the exit hole of the suppressor that you can,it makes a huge difference.
As for making the filling, I have tried punches to an extent, but nothing really beats a good pair of scissors and a couple hours to cut foam.
I like to have a sharpened aluminum tube such as a piece of arrow, and I like to put little notches in the sharp end with a knife, so that it can cut more like a saw and cuts very cleanly.
I then wrap painters tape on the tube about 2 inches up from the sharp part, and I make it so that it is a tight fit in the suppressor of choice.
I then line up the tube on top of my foam so it is perfectly level, and I twist away until I exit the other side of the foam.
Then, I trace around the tape with a marker onto the foam on both sides.
I then cut out the piece leaving about 4mm of waste around it, and I slowly and very carefully cut it off to line up with the traced circles until it is perfectly symmetrical.
I prefer 6.5 and 7mm holes, but I your case you should start off with at least 8.mm as you have never made a suppressor before.
Besides that, try to decrease the inner diameter of the exit hole on the muzzle of your suppressor, I used a lathe and made a hardened steel insert that shaves off extra air and sound, but you could probably use tape wrapped around a larger diameter drinking straw.