I remember at one point thinking I would rather die than carry on feeling so ill
This is actually what you need to cling to. You didn't feel tired, you didn't feel unwell, you didn't just feel sick - you felt so ill that anything, anything seemed preferable to carrying on.
People who haven't had sickness can sympathise, but they can't really empathise. It was the worst I had ever felt in my life, and it was certainly bad enough that when I saw that positive pregnancy test my only though was "I can't, I really can't, not now."
But as others as saying too, you don't have to write future children off. Your son will change so much and when he is older it may seem more manageable.
But if you decide you can't go through it again? That's equally fine. I know before I had DD I always wanted two children. After that pregnancy, I wouldn't be devastated if we weren't able to have another.
Please be kind to yourself. People on here understand why you made that decision, I promise you, and you are certainly not alone in making that decision. That is what you need to remember. You're not alone, in any way, even if it is hard to talk about it in RL.