Just did this route from cycle.travel https://cycle.travel/route/london_to_brighton
It's great, almost entirely little roads, skips round the slower climbs and really follows hill ridges so you get nice long descents.
Bit sweaty and difficult in >27 degree heat, and if you're a pretty leisurely cyclist I would not describe it as "easy". Also there are a couple of sections of gravel/slightly muddy paths that you would struggle on with <=25mm tires but they don't last long and they help miss out hills or annoying roads.
Would give the route a 10 out of 10, also gpx/printable map/instructions on the website makes it easy to follow.
-- there is a nice spot half way up ditchling beacon to the right of the road next to a fence/gate/stile that you can collapse on for a lucozade/whiskey/lie-down. Worth making to it there rather than stopping in the road earlier later (if you're not going to do the whole thing in one)