Help to Purchase my first Apple Watch with ECG capabilities

Hello,

I am a female senior and I am looking to purchase an Apple Watch that will give me a good fit to assure good results when using the Heart Rate app and ECG app, and is capable of obtaining AFIB reporting and can be used while swimming. I have a very small wrist, and small pocketbook, so I am not looking for the most expensive choices.

Can you give me suggestions what the quickest way to locate which watches meet this criteria on the Apple website please. It's a little confusing.

Thank you.

Sue