@ThatOpalSeal hi there, hairdresser here. Don't wait, by waiting you will have a harder time getting your hair back than if you look after it and help it be the strongest it can be now, into and through your next pregnancy.
What I would advise though is it not just a one product will fix all situation. I would recommend you get your bloods checked to ensure you're not deficient in any nutrients, make sure your eating a varied and balanced diet, take a multivitamin, drink plenty water throughout the day, get a little exercise each day - doesn't need to be strenuous, a walk will be enough to get the blood flowing, and as much rest / sleep as you can. All these things help your hair that is being produced now be as healthy as it can be, and grow at its optimum speed for you.
I started using my scalp hair growth oil immediately post partum, my hair multivitamin and walking daily where possible. Obviously getting lots of sleep was impossible with a new born, ensuring I was eating a varied and balanced diet was hard and water intake was also difficult to do most days, but we just have to do all we can when we can. I did lose hair - there is no way to stop it as it's our scalps returning to normal, however, the amount and for how long is effected and was the minimum loss for me, my hair loss had returned to normal by around month 8 and all the baby hairs growth is both hilarious and annoying 😂. But my point is, do everything you can now to look after your hair and get it into its strongest and healthiest state ready to face pregnancy when you do have another and then start back on it straight away post birth.