I go along with the comments already made about the clothing, pack, and bag. For 3 season I go with a 30F to 35F bag and carry very little in the way of extra clothing. When temperatures are marginal I add an MLD Soul side zip bivy.
Thom made an excellent suggestion on the MLD Grace Solo tarp in Spectra. I have one and augment it in bug season, or extremely inclement weather, with the MLD Soul side zip bivy. Having said that, I used a Contrail extensively prior to making the full time switch. I believe that the Contrail is the best full featured shelter on the market. It takes a "Leap of Faith" jumping from a full shelter to a tarp and each hiker will make that decision only when he/she feels confident about it.
Stuart... in response to you're last post. The Grace Solo tarp is almost as easy to set up as the Contrail. It always takes me 60 to 70 seconds with the Contrail, and the Grace is comparable. They set up in almost the identical way and could certainly be done one handed. I sometimes take a little extra time with the Grace since I'm a little fanatical about getting it's tension perfect. It does take two poles, though. I use the TiGoat AGP's at 6.4 oz per pair, and they work perfectly with the tarp (or the Contrail).