Of course YANBU.
I would stop and run through some of the practical scenarios that may occur over the years, as that's at least what MN can help advise on.
You can try and create your own support network. As long as you put yourself out there a bit during your maternity leave you will make friends and find contacts of people who can help you. We knew no one in our local town when we moved heavily pregnant, and we've made friends we could call on in an emergency.
As you don't have family close by (what about friends, though?) then I'd want to think about some of the real practicalities that might crop up over the years.
What's your maternity package like? What will your employer be like?
Will you be likely to get flexible or part-time work if you request it?
Generally childcare is available during the week between 7.30-6.30, would that fit with what hours you work and your commute?
Can you afford to take a hit of anywhere from (complete ballparks) £600-£1100 a month in childcare?
If your child was ill with something like chickenpox, which can require anything up to a fortnight off childcare, would you be able to juggle work?
Plenty of people are single parents with little support and do an absolutely amazing job. There's no reason why you shouldn't chose to do this if you want to. But as I keep saying, there are some practicalities that are worth seriously considering before you start down the path.