You will be able to pick your seats from 7 days out as a OW Ruby even on a basic economy fare. Apologies for stating the obvious here but bear in mind though that there is no checked luggage with these tickets though, just the cabin carry on limit.

Adults, young adults and children

1 handbag/laptop bag (max. 23kg / 51lb and up to 40 x 30 x 15cm / 16 x 12 x 6in)

plus

1 additional cabin bag (max. 23kg / 51lb and up to 56 x 45 x 25cm / 22 x 18 x 10in)