You have a few options to get more followers. Airdrop, Giveaway contest or classical social media campaign always can help.
You need to attract people to follow your social media channels.
I do not recommend any kind of direct followers buying, you will get only fake profiles with zero audits.
True! Buying bot followers won't help project. Having thousands of followers but 2-3 engagements on tweets will look so bad.
Best way to enhance Twitter organically and cheaply at the same time is Giveaways. Although you won't get 10K followers via Giveaways but such 1K-1.5K engaging followers will be hundred times better than 10K Bot Followers.