I also sew with silk. I use French or flat feld seams.

interfacing!!! it really is a must when working with satin or silks...and it really adds great stability without changing the hand...as long as you get a lightweight one...a woven lightweight interfacing will hold seams together for the long-term and make the fabrics lots easier to handle.
good luck
i use interfacing with velvets too...any fabric that is stretchy, silky/slippery, tends to move around or stretch out of shape interfacing is the answere.

Always do some sort of seam finish, either zig zag or srege the edges. I am a former bridal seamstress and seam finishing is a must.