Please help a completely clueless girlfriend buy keycaps for her boyfriend!

Hi! I’m very new to keyboards and key caps but I’d love to buy a cute key cap for my boyfriend. He has this Ducky mechanical keyboard and I was hoping to find some resin artisan key caps with koi motifs. Ones I saw on Etsy that I like were this and this for just one small key like “escape”.

How will I know that the key caps will fit and be aligned with the rest of the keyboard? Is there a certain “number” or “name” for the kind of keys the Ducky keyboard has? I’d love for it to line up perfectly (height and shape wise) with the rest of the keys as my boyfriend’s a bit of a perfectionist. Do you know any better places to buy keycaps (preferably with shipping to both Canada and the US) or is Etsy a decent place to purchase from? As for budget, I’m not too sure about the average price of an artisan key cap but I’d prefer to keep it below $50, if possible! Please let me know if this isn’t the right place for this question and I really appreciate all your help!