I’ve opted to send through some products with the best documentation and fastest avenue to success rather than what might be the highest performing.
(From this guide) Arduino SELF-BALANCING Robot - Hackster.io
Along with a battery this collection of parts ought to get your hardware sorted out.
My class at uni made some balancing robots from the ground up using a more engineering approach rather than the Maker way of throwing a PID at the problem (and hand tuning).