I'm trying to use Avios to fly from IAD-CDG (31 March) and return from LHR-IAD (11 April).

I'd like to get a premium economy seat for outbound and inbound, however there is nothing available from LHR-IAD.

If I book the 11 April trip now, is there a chance premium economy will become available later or should I wait another week or two to see?

I am a neophyte when it comes to booking flights with awards and it makes my head spin. I just want a small upgrade to make the flights more bearable.