Hi Jim. You say you're a purist and like sustain, so the obvious pedal choices, IMHO, would be a compressor and a boost pedal. Both will keep your tone but will enhance the guitar's responsiveness and increase sustain making playing easier and your sound more even and consistent - a more 'recorded' sound, if you like. The booster pedal is a very subtle overdrive that just adds a little more drive and life to the tone without being obvious 'distortion'. I would try the real cheap eBay $30-60 pedals from manufacturers such as Mooer, Kokko, Donner, Mosky etc al. If you like the direction they take your sound and playing in, you can always spend a little more in the future buying replacements with a littler more class. Have fun Jim! Joe.