Hi hun.
Right first of all, take a deep breath

Ok, my mw always told me to feed from one breast and then use the other one at the next feed if it is more than an hour later. If the next feed is within an hour, just use the same breast. If your lo is falling asleep during the feed, change his nappy or strip him off so he doesn't get too cosy and is a bit more alert.
Not everyone experiences the let-down sensation, when i get this i feel like my boobs tense up slightly and i get a tingling sensation. I think (and i am sure someone will correct me if i am wrong) that the let down is when your milk starts to flow a bit faster, making it easier for your baby to get the milk.
If you are feeding regularly your boobs may not feel hard or really full. They tend to feel like this if your baby goes a bit longer between feeds than usual. Although some women don't experience the hardness etc. It is perfectly healthy for your breasts to be feeling soft, it means that there are no blockages. The size of your breasts and how hard/soft they are doesn't really have any bearing on how much milk you have. Every woman is different!
Just relax, you are doing a fab job
Lx