I have been forced to quit lattes entirely because my baby is sensitive to milk (sob)... but last year I decided to get my habit in check. It was becoming outrageous, because our supermarket had a Starbucks right inside the front door. I may not have been able to get out much with my toddler, but I was certainly making it as far as the supermarket a few times a week!
I bought a Starbucks gift card and made that my limit. A $20 card is five lattes, give or take. Once that was gone, I couldn't get more until I could add more $$ to my card.
My big scheme for adding more money was to use the "Coinstar" machine in the supermarket, the one that counts your change for you. On our machine (I haven't seen this on every one) there's an option to get your coins counted without a fee if you put the balance on a gift card. Starbucks is one of the options.
We keep our loose change in a jar in the kitchen, and every couple of weeks or so I would take the contents of the jar and add it to my giftcard. It usually worked out to about 1-2 lattes per week -- enough to satisfy my jones and keep it a 'treat'.
Now I have about $30 on a card in my wallet, waiting for the day when DS can tolerate the milk proteins again, maybe next year?