The best setup would be an integral suppressor. This would require a dedicated/modified threaded and ported barrel, relieved stock, and the suppressor housing (or can).
Most sound suppressor designs for rifles shorten the barrel to lower the bullet velocity to subsonic and mill ports in the barrel to allow gas to escape.
You might attempt to make your own suppressor with the proper licensing of course, but some of the designers out there are so good (Dater, Gemtech) why waste the time and energy.
I use .22 Long CBee caps. Yes, the range is short and the accuracy is substandard but they are useful and effective in certain situations... You may have to cycle the bolt manually... Give these a try before going all out on the suppressor thing.