Preparing for mobile on new website

I’m about to embark on a redesign of a website and will be using WordPress. No problem there. However, I need to make this site mobile accessible and I haven’t done that yet. In reviewing the plug-ins for mobile, there are many options and I’m not sure what to look for. Many of them seem to be enough for what I need but I don’t know how to evaluate them.

Is there a guide or some place I can go to understand better what I should do to prepare for “mobilizing” this new website?

The site will be used by victims of domestic violence so it will need to be easy and accessible for someone via smart phone, regular phone and internet.

Thanks for the leg up on this. Apologies if there’s already a post but I didn’t find it when searching for it myself.