What Pokémon Game Should I Get For Gameboy?

I really want to try a Pokémon game because ive NEVER played one before and people say how good they are no matter what age you are. I’m a 16 year old girl who loves gaming and has started looking into Retro gaming, I only bought my gameboy yesterday and i love it so dont say get a ds because i sold my ds and im not getting one again. I have no idea which ones are good.. Can be gb,gbc,gba i have gba sp.
ALSO – Where can I buy cheaply? Amazon & Ebay are like £10 per game