Hi bsb7140,

I fly the SQ A350 often. For two seats together, I would recommend 11D/F, then as a second choice, 19D/F, exactly for the extra legroom while sleeping reason. However, if in 19D/F, make sure you ask for earplugs (or bring your own) and wear the eye-mask as the galley is right in front of Row 19 and has kept me awake from the light/noise (albeit minimal).