Taking too long to load first byte

[Ollie]

My website is taking about 4 seconds to GET store. I already changed the driver from mysql to amysqli and enabled Turbo cache with the webhost, but these steps haven't helped improve the first byte load. Is there anything else I can do to make it faster? The total page load time can be as low as 9s and as high as 40+ seconds, depending on how busy the server is. (I use a shared server.) I'm in the process of optimizing images, minifying scripts and deferring whatever scripts I can. I use v. 1.2.0 with tons of customizations and I'd rather not upgrade. I'm also trying to stay away from CDN as I had some a pretty bad experience with CloudFlare (constant 404 errors).