what is your end goal in terms of when it would be easiest to breastfeed? Are you looking to have a morning and night session only? Or would you be open to having a morning, and 2 evening sessions? I ask because if you can nurse 3 times in 24 hours you don't have to worry about cows milk or formula.
And I think that dropping one session a week is a very good and realistic goal. I would start with sessions that are already the shortest. Leaving the ones you intend on keeping (perhaps morning/evening) and maybe dropping the ones closest to meals last (to give your lo more practice with solids before he really has to rely on solids, kwim?).