OP, I could've written your post just over a year ago :)
DS was 14 months when we relocated overseas. We spent 6 weeks living with my DM, and then moved to the other end of the country. 3 weeks after the second move, I started work. A few months after that, he started daycare fulltime. (About 3 weeks in, we realized it wasn't working so he changed daycare...) AND we've just had DD (DS is now 28 months.)
I would say the run-up to the move was far more stressful (for me, and by extension for him) than the move itself IYSWIM. We sold our house in England, but had a complete nightmare trying to complete (long chain, things kept going wrong further down the chain and it was all really uncertain, then looked like it was all going to fall through and we didn't know if it was all going to work out until we exchanged and completed 4 days before the removal men came... We'd had to book without knowing as it was right before xmas and we really needed to move before the holidays...) and this was all after having had the house on the market for 10 months, with constant viewings and trying to keep the house presentable. Anyway, it was all unavoidavle but I wish I'd have managed my stresslevels better.
When we did move, DS was right at home at his granma, because we'd spent a few weeks there over the summer. If there is any way you could at least visit the GPs before the move, that would be great as it would then be a familiar environment. DS is a sensitive child, and although he's always found it easy to adapt to new situations WITH me (we co-sleep and BFd extendedly) we felt that it would've been too much for him to go to daycare after the second move, so DH stayed at home for a few months after I started work. Luckily we could just about afford this... Because of all the changes, we carried on co-sleeping and BFing, probably for a lot longer than we might've otherwise. Not sure if you do either of these, but if you do, do think about extending it for a while perhaps.
DS has a particular teddy which he quite liked, but I did start encouraging having the teddy in bed etc. before the move... And DS has found the teddy a comfort, takes him to daycare etc so as others above suggested, having a comfort-object might make the transition easier.
Oh, also packed tons of his favourite foods and snacks so that his diet wouldn't change drastically when we moved. (He went through a stage of refusing anything home-made and excisted mainly on Plum organics for a few weeks...)
All in all, the moves and changes went a lot smoother than anticipated, and DS didn't really show any signs of stress apart from disrupted sleep... But he's been a terrible sleeper since day 1... And he obviously also had a new language introduced as he started daycare, but was speaking it within just a few weeks!
He's welcomed his little sister with open arms, so I'd say it's all likely to be more stressful for you than for him - but try not to worry and enjoy your new life, it'll soon be homely and comfortable for all of you!