https://en.wikipedia.org/wiki/Section_508_Amendment_to_the_R...
The basic stuff, like adding alt tags to images that have meaning and "skipnav", so readers can choose to skip directly to the content of a page without re-reading the navigation, are actually pretty straight forward to implement.
After you retrofit a site once, you'll find these things don't add much time as you incorporate them into the process the next time.
It's actually more about not disabling the accessibility features which so many web designers do. They're all built in and meant to work almost seamlessly alongside your design process, but people disable them because they are so self-centered they can't conceive of how someone with a disability might feel using their website.
Accessibility has been built in to the web for a very long time. The design process is "If I were blind, would I still be able to use this website? If I had mobility issues, would I be able to use this website?" Then you address those uses cases.
- What happens if I can't see this image?
- What happens when I disable focus hints and keyboard shortcuts?
- What happens if someone needs larger or smaller text on the page?
It's not a "kind of" design. It's just being considerate to other people's situations.
But really, the magic word you're looking for is "accessibility" (or "a11y" (eleven, not LL)) - spend an afternoon with that word and your favourite web search site.