http://www.ldlines.co.uk/
Portsmouth - Le Harve is good as they do an overnight crossing, ship leaves about 11pm and gets to France for around 7am (6uk time) so can get a nights sleep and start off fresh. You can either sleep where you want on the ferry, last time I did it was on floor with roll mat and sleeping bag, or you can get a cabin for extra.
not tried other routes.