Selle Italia have a sizing guide tool that you can use online to figure out what type/size would suit you best and it is reasonably accurate for most.

I have a Selle Italia Carbon Superflow SLR that weighs only 122g so hardly any padding to speak of and it is very comfortable on 200km+ rides. So saddle type and size is very important and padding need not be much at all.

My preferred clothing is Castelli and Santini, both make comfortable kit across their ranges. The combination of a correctly fitting saddle, a good bike fit and decent clothing allows for all day on the bike.