Do you have shares in Eurotunnel and get a discount? Otherwise the ferry is much cheaper. Most of those of us who are regular travellers use Norfolk Line to Dunqurkue. Yes it is farther east, yes it takes longer, but as it carries more lorries and caravans than the Calais route there are few (if any) children running around, the boats are all fairly new, well equipped, and quiet, and - above all - Norfolk Line know how to look after their customers. Once over the other side there are plenty of places nearby to the ferry terminal to put the legs down and get some more sleep f needed - you will have had possibly a couple of hours on the boat and you can arrive on the docks in Dover up to two hours early as well.
When you add up the waiting, queueing, and getting on and off, there is really little difference between rail and ferry - unless it is poor weather!