You will naturally be closer to your eldest and proli give them the moon on a plate should they ask you too!
We didn't have any more babies until my eldest was 8 years old, and we decided that the best thing to do was knock out 2 in 2 years so they could grow up close and with each other blah blah blah.
I thought I may damage my eldest as although he had play dates and stuff he didnt have any siblings or cousins he could see regularly.
I was wrong, my 2 smaller ones fight all the time they don't play well and well on my worst days I've wondered if I'd like to rewind 5 years or fast forward 5!
I love them all the world that goes without saying but sometimes one just works.
With 1 we had more money, more time and a fuck ton of patience. We had more time together for family dinners, trips, managed to go shopping and 1 child is easier to pick up drop off from almost anywhere.
You will often find babysitters are hard to get hold off, family will go silent because suddenly you its not just one child for 2 hours but 2 or 3. No one wants to babysit a brood 
Things like school plays / sports days / come in and buy this paper your kid touched 3 days ago for £5 are much much easier to attend, if you have 2 kids in 2 seperate years or 2 seperate schools time is right and only so much annual leave you can take. Even if your a SAHM it can be a very repetitive chore.
Less mess!
There are SOO many pros to not having more than 1 child. There are cons too but you know this.
If you really really wanted one I wouldn't put just a years limit on it, unless its affecting you massively id go for a little longer but maybe less 'determination'.
It can only ever be what it will be but i hope you get your wishes and have a lovely life with one or two children.