Hi all
I'm looking for a fare to go:
Flight 1: London -> Los Angeles 21 Dec or next day
Flight 2: Washington -> London 3 Jan plus/minus a day

My preference would be Premium economy each way.
I've found a fare for £1034 on Kayak but this doesn't seem to be bookable.
I've also found £1207 on Google flights, but again, going onto the BA website this doesn't seem to be bookable.
On the BA website, the outbound flight shows as £565 in WT+ and the inbound at £719 so not a world of difference but it is there.
It also offers Club class for £791 on the inbound leg. so I for the sake of £75 I thought I'd go for the flat bed, so selected the outbound at £565 and the inbound at £791 expecting the total to be £1359, but the total came out at £1750

Am I doing something obviously wrong here? I don't really get how I select two individually priced legs and then the price jumps up by £400.
All advice gratefully received.