I'd agree with jec6613: Check if the flights you'll be on offer MCE (labelled "Main Cabin Extra" in the seatmap). If yes, save your Avios. If you have any sort of status on BA (Bronze and above), you have access to these seats for free. Just bring your own inflight entertainment (all MCE seats have power) and food will cost you extra.
While MCE is not BA World Traveller Plus, it's actually quite nice as far as economy goes. Definitely tolerable for a transcon flight.