Hi there! I have been using the bags since my daughter was 8 weeks and they are great, shes also just over 4 months old! I would recommend that you get the 6-18 mth bag seeing as he is only a few months off 6 months. I also would probably get a 1.0 TOG. I am in Melbourne too and have been using a 2.5 over winter but am about to buy her some in a lower TOG as the weather gets warmer. Although its not recommended I use blankets and sheets over the bag as I just find that the recommendation on the bag for what they should wear for 16 degrees is far too little. You can always do the same unless you dont want to put sheets or blankets over the top. I remember when she was first in it her feet only seemed to come down halfway and I think you will find the same for the 6-18 month one - as long as its secure around his shoulders and head and he cant slip down, dont worry about the length! HtH and welcome to Belly Belly!!