If your Dr has reduced your MH medication because of your pregnancy, have you had counselling or a therapy group put in place to deal with the withdrawal symptoms? I suspect that at 9 weeks pregnant, you have not accessed all the ante-natal/midwife support you will receive ultimately.
You really don't have to make decisions about dogs and carpets at this stage. In fact, should you choose to have the baby, your decisions may be very different to those you would make as a couple. (For example, I would never get a dog BEFORE a baby comes into a family.)
Counselling may also help you to communicate better. But you might find that communication resolves itself once your DP moves to the UK at the end of the month (you said arguments only started when you moved back to the UK).
I actually think that I actually think I'll be a terrible mum could be the crux of the problem. Just because your mother was a terrible Mum does not mean that you can't be wonderful at motherhood. Some people find it comes naturally, others need help because they have no-one to mirror. But at the end of the day, if you know you want this child, then help and support is there to help you to become the great mother you want to be.
If, when you have weighed it all up, the decision is entirely yours. If you need help with your decision you can contact support services who can assist.
I'll leave you this link in case it helps you:
www.plannedparenthood.org/learn/pregnancy/pregnant-now-what/thinking-about-abortion
Good luck.