Night feeds

Janine
My son is 12 weeks old, he goes to bed at 7pm and has two night feeds (between 11:30-1 and 4am). He is exclusively breast fed. 
Any tips on how I can slowly start encouraging him to drop one? 
Also, for his night feeds he falls asleep nursing. Am I creating a sleep association by doing this? Should I wake him up after each feed before putting him back into his cot?