Honestly OP I don’t think I would in those circumstances. If you can only at a push add £300 per month to savings, then I assume that’s all the spare cash you currently have each month? Obviously that’s still a lot of money, but when you consider you’d have an entire other human to support, it’s tight, food, clothes, milk, nappies, wipes, childcare, after school clubs etc. The £400 from family will help initially but your child will still be expensive at all ages, as a single parent you will likely need to use breakfast or after school clubs once they are in school and that isn’t cheap.
I’m currently pregnant with our first baby and we did lots of finance planning before ttc, I am on a very similar salary to you and based on the figures we came up with, I wouldn’t have done it alone as it just would have meant a life of worrying about money.
Plus the “set up” for a baby isn’t cheap, DH & I have both been shocked to see how expensive everything is. In addition, I truly don’t know how I would have gotten through pregnancy without my DH. Although it is the best thing ever it has also been the hardest thing ever in ways I could never have imagined, without his support I would have really struggled.
I think other posters have the right idea in freezing your eggs now if possible so you have the option x