Doesn't look like BA screws you for a one-way either. Currently a lot cheaper for the dates I need, especially when you consider baggage fees.

Read enough horror stories about RyanAir to eliminate that option from consideration.

For the sleeper, is it possible for one person to purchase 2 of the bargain berth tickets, so as to keep the cabin to myself?

http://answers.loco2.com/3cf-how-to-...n-berth-ticket

That site describes that they release a limited batch of tickets.