I too am overseas, no support network, and dh working in another state for 1-2 wks at a time after pat leave (2wks). 15mths between ds3 and ds4. Would second that a brilliant double pram is an absolute MUST have. I still walk between 4 and 8kms daily with mine. Walking saved my sanity - loads of it. Mothers groups were also a godsend. Having to be out the house before 08:45 every day to take ds1&2 to school really helped - forced me to have a routine. I swear by routine, would probably sink and burn without it
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I always tried to ensure that ds3 was cosied beside me on the sofa with film on/books/toys while I bf. Ensure toddler is gated in with you while you feed, to stop him shoving stuff down the loo/rearranging the kitchen etc.
Invest in a good playpen or baby dan to either cage in the toddler, or lay baby in on a mat to stop toddler jumping or falling on baby (or, as happened to a friend of mine, pulling over the Moses basket) while you nip to the loo.
If toddler is still napping during the day, use that chance to get you and baby's head down for thirty minutes. Power naps are your friend. Also, batch cook while you have your other half at home, to ensure you always have easily accessible nutritious food available. Sandwiches get boring. Keep your fluid and food intake up, to help with energy levels. Lastly, enjoy! It's bloody hard, but so worth it. 