Best wearable tech to track sleep and heart?

Hi! I really need to track my sleep better, and heart data like variability would be helpful too. What’s the best wearable tech on the market for this? I’m only familiar with the Oura ring and Apple Watch, but don’t have either. I did some research online but couldn’t tell which was best in the sea of products. Please recommend products and models! I have an iPhone, if that’s relevant for compatibility. I’m ready to spend whatever I need to, but I would like it to be on the right product!