Choosing an Optimized Theme for My WordPress Site

One year ago, I chose a random simple theme for my WordPress site. It isn't very optimized and I believe it's slowing the loading speed. I want to switch to another theme that is optimized for speed and SEO.

I am thinking of Astra. I read that it's built with speed in mind. What other options do I have?

I use shared hosting so I think theme builders, such as Divi or Elementor, would further slow my site.

Thank you guys in advance.