Mulligans
General Mulligans
These are mainly the cards that you'll want to go for. Since you'll be forced to play behind for a bit, early board presence and removal are keys to success. Make boards with dreamway and landscaping, remove early threats with bees and wrath, and generate value with worthy and crystalsong. Once you're finished with the quest, immediately pop off with Oasis Surger and Nourish.
Aggro Mulligans
This is the one matchup where nourish isn't a very good option to mulligan for. Hidden Oasis is much more valuable for you against aggro because you heal for a lot and put a decent sized taunt minion on the board. By the time you're in a good position, the game should be over by then, since your opponent will have most likely ran out of gas by the time you get to that point.