Congratulations on the birth of your baby!
My son is ten months and he's never had a heated bottle. This has raised a few eyebrows but he is no worse off as a result. He was a week in ICU from the time he was born and so was tube fed for a while. When they did start feeding him it was from the pre-made bottles, which weren't heated.
From the beginning we would boil fresh water, leave it to cool and then fill bottles. So when you need to give a feed, all you have to do is put in the formula. We still do the same now. And the cartons are great to have as well, especially when you're out.
It's tough being a new Mum, so do whatever feels best to you - don't be worrying about what other people think! And enjoy your baby!