Directions to Crystal Palace site

mitten

I am going to visit the Crystal Palace site for the first time next week and would like any helpful suggestions for the best route to take, travelling from York. I am staying overnight near Bedford and so an approach via the M1/M25/M4 might be the obvious
one looking at the map.

Handbook directions start on the A205 south circular so I need to get to that point.

Any suggestions would be great.