I'm so sorry you're going through this. I had a termination at 22 (coerced by my partner and thought it was the right thing to do at the time, felt I had no choice, etc.). That child would be 22 now. I'm married with a 13 year old and a 7 year old with profound SEN. I understand your pain and your sadness. Personally, I bitterly regret my decision and if you feel that way (given enough time to heal and move on with your life and family) then please seek support. There are counselling services that are excellent.
You may feel much better once your body adjusts as you are clear in your reasons, your age and your other children are important in your choice, for instance.
You did what you thought was right and you made your decision for some sound reasons. That said, of course it will never be that simple, it's just not. It's an awful, painful thing that comes with so much guilt that you don't feel you can share it and the feeling that it's too late is heavy.
At the moment, your hormones are all over the place and your body is coming to terms with the change. Emotionally, you're very fragile and you're questioning things because it's natural.
You aren't a bad person, or a bad mum. Your hormones will settle and things will seem less raw and less tragic in time. I can't say it gets easier, as you asked, because it is very personal. Please don't be hard on yourself or go over things that can't be altered and give yourself time to heal. I hope your husband is supportive. Was he included? Is he aware you are struggling?
I may not be able to get back on tonight but I know some lovely MNetters will be along shortly to give great support. Please be gentle with yourself. Gentle hug. 💐