Hello -
Congratulations on the birth of your baby boy and well done for breastfeeding! I can highly recommend expressing to give yourself a break, I started when my son was 2 weeks old and he's had an expressed bottle almost every day since (he'll be 25 weeks tomorrow). I heat expressed milk the way Luce suggests, and check the temp by spraying a couple of drops on the inside of my forearm (or I did when I first started expressing, now that I've been doing it for 5 months I can just tell from the feel of the bottle but I wouldn't suggest that method for grandparents!). As Luce says, the main thing is that it isn't too hot, my baby certainly doesn't mind slightly cooler milk but then he's a greedy monster who'd eat anything! If it feels slightly warmer than tepid then that's fine but if its warm enough to heat your hand when holding the bottle then it's too hot.
If you manage to express enough to freeze you can get freezer bags from boots - if you freeze the bags lying flat they defrost and heat to the right temp in less than a minute. The important thing is that you under no circumstances heat the milk in a microwave as it denatures the proteins and they don't know what longterm effects that will have on baby's health.
It took about a week for me to manage to express enough for a 4oz feed (the first few times I only managed the odd ounce), and I found it was easiest to do immediately after the first morning feed (one boob for baby one for bottle) but you'll find your own way. I can now manage to express 8oz in one sitting but I only do it once a day. I use a Philips Avent manual pump, but some people swear by Tommy Tippee and others prefer an electric one, have you decided what you will use?
Good Luck, it can take a while to get into a routine of expressing but you won't regret it! Some clever people even manage to to express at the same time as feeding but I certainly haven't managed that yet!
Hugs to you and your baby x
