To find a simpler dun mayfly imitation will be difficult. All you need in the way of materials is one long fibered CdC feather and a short foam cylinder and a hook.
I named the fly “All In One” as the whole fly is tied with the same one CdC feather. You need to practice a little if the techniques I us are unfamiliar too you, but with a little practice or after you have tied a half dozen or so, it only takes about two minutes to tie this simple but effective pattern. All in one floats fantastic as the whole fly is made from CdC and foam.