I just have a spreadsheet, each tab is another python. And it's on google drive so that my housemate can access it.
The columns: Date, Snake Weight, Snake Length (approx), What was offered (size and if rejected), Feed Weight, Notes (ie shed, increased feed size, vet history).
We don't weigh the rodents every time, we often use the average of the size. I pay more attention to the snake's weight than length. Length is more of an opportunistic thing for when the snake decides to spread out along the edge of the tank. (my coastal doubled herself over against the side of the 1.2m tank at one point, so we know she is 2.3m, but she's the only one we're sure about.)