Stocks are a ` middle-of-the-road` solution usually, and to the best of my knowledge, all vendors only supply a medium density in a stock...... they also may not ` fit` very well at/around parts of the perimeter and can have pleats or puckered-up bits/sections, due to the curvature of your head not being the same as the stock,so just to be aware of that. Some guys get a perfect fit with a stock, but generally, they are in the minority. If you still want to go with a stock, you can easily thin a medium down a bit with this method..... http://www.youtube.com/watch?v=rPULkcyVD2Y
I don`t want to put anyone off ordering a stock--they can and do have a role / be useful, but there can be limitations in terms of fit as I outlined, but they can ease you into wearing, or get you out of a ` bind` while waiting on a custom-fit system. Hope that helps.