What is the best way to transfer the hosting provider for a WP blog that has been indexed for 15+ years?

I have been getting lower traffic for my old blog with over 1000+ blog posts, What do you recommend is the best way to switch hosting providers?

I already have the backup hosting provider available. I know while the Nameserver change, my emails would break etc. I want to understand what are the things I should consider while I do this.