When your basil ambitions outgrow your actual basil plants, it is entirely acceptable to cheat a little. I would go so far as to call it sensible.
Pick up a few healthy plants from the garden centre or even the supermarket, then immediately rescue them from their rather cramped little lives. Rehome them into a pot two or three times larger, with decent, proper compost rather than whatever sad stuff they arrived in.
Give them a warm, sunny spot, water them gently but regularly, and then start harvesting the top tips quite early on. This feels slightly brutal at first but it is exactly what encourages them to branch out and behave like proper, generous basil plants rather than lanky little stragglers.
Every now and then, treat them to some indoor plant food, as if you are quietly bribing them to perform better, which in a way you are.
Do this and you will be rewarded with plants that turn into exuberant green fountains, giving you three to five generous harvests each over the summer. Perfect for topping up your seed-grown efforts and rescuing you when your pesto enthusiasm outpaces your gardening skills.
Talk soon,
B x