Hi Bec

Jesse (DS2) was a very hot baby - still is. He sweats on a relatively mild day! When he was a little baby I just made sure I fed him more often and made sure his room was cool before sleeping - he has a fan in his room and an airconditioner in the lounge reaches his room which I would put on about half an hour before he was due to sleep. I also regularly wiped him over with a cool flannel. I made sure his cot sheets were cotton and on really hot days/nights he slept in just a nappy. When we had to go in the car I made sure I put the aircon on well before we left so it was cool inside. On really really hot days I tried to avoid going out - but thats not always possible. Im not sure how you get Xavier to go to sleep but if possible I think it is helpful to get him in the the habit of going off to sleep on his own so that you dont have to rock him to sleep which would make him all hot and sweaty in your arms.
I am sure you know and do all of this already but I HTH in some way and good luck!!