We are redesigning our website and there are some concerns internally that accessibility affects the design element. A toggle mode was suggested. Our standard version would
Are you sure what you really want is a toggle? This is forcing an extra step on some users to use your site. This is specifically concerning as you are talking about toggles for contrast ration and font size.
From this I can presume that you have some parts of your design that have poor contrast and small lettering.
For starters people who have issues with contrast and font-size aren't just "traditional blind people", but also:
Additionally, small fonts will make it difficult for phone and tablet users (a very quickly growing market).
If your issues are with contrast and font-size, I'd suggest re-exploring your options to improve your design as it will probably impact many more users than you realise.