Hi Katy :o)
we took Jacob out to Spain when he was 10 weeks old. The weather was unusually hot when we went out, but you'd be surprised how easily babies adapt to the climate once they are in another country.
I was breastfeeding, and found that if Jacob was thirsty he would latch on for a short feed to quench his thirst with foremilk. We kept him out of the sun, period. A shaded babe is a happy babe!
Because your little one will be older than Jacob was, make sure you have a bottle with some cooled boiled water in for baby to drink if you are concerned about dehydration. You can flavour it after 4 months, a tea spoon of fresh fruit juice in 5oz of water should be enough to encourage baby to drink if they won't take water! Alternatively you could give it to them off a spoon.
So far as routine goes- babies are incredibly adaptable, there's no reason for your routine to be greatly upset by being on holiday! As long as you keep the basics like morning feeds/bath time/evening feeds the same I wouldn't think baby would cause you any more problems than usual!
The villa we stayed in didn't have air conditioning either, but like I said, keeping baby out of the sun is the easiest way to keep them cool.
Invest in a cheap inflatable paddling pool! We used to put Jake in his to cool down if he was getting irritable from the heat. Alternatively- a tepid bath is also good!
Dress baby in the minimum- nappy, t shirt & hat is enough!
And no matter how shaded you keep them- a high factor sun cream is a must, go for the Garnier Ambre Solaire Kids 50+ spf - yes it is more expensive, but you can't get any better protection for delicate skin. Ideally apply it before you leave the house, and when baby is in just a nappy, even if they are going to be wearing a tshirt as well.
I would also recommend a parasol that attaches to the buggy- bendy ones can be adjusted to shade baby wherever you go, and are universally more effective than the existing hood on most pushchairs!
I hope this helps :o)
MG, Jake & 35wk bump