Has it eaten a rat pup lately? Sometimes once a snake is used to getting mice with hair switching back to something like a rat pup does not work. It would be terrible to order a bunch of pups and not be able to use them. If it were me I would order some large mice, weaned rats, and maybe small rats if you have the freezer space and money.
I usually order six months at a time. But it goes alittle further because I don't feed during shed so each snake stretches the time out since I don't factor in shed time. As for what you should buy its hard to guess. Each snake will grow at a different rate. I would guess that a few months of large mice would get it up to weaned rats, and a few months there you would be ready for small rats. That is only my guess.
I can tell you my bp made the move from mice to small rats in seven months. Half way through I was feeding one mouse and a rat pup which would have been close to a weaned rat. I did this because I had extra rat pups and weaned rats were not available at the time. This was one feeding per week.