You should ask the Contact Centre for the N fare. This is usually the cheapest at 10 TPs and can be not much more than O/Q, depending on circumstances. N can be for both Basic (previously HBO) and Flex (checked baggage) bookings. In addition to the extra TPs, it can be upgraded to Club Europe for Avios if required. Since this can be done to an Basic N fare this would thereby grant you checked baggage and seat selection with status. There may be a Contact Centre fee for non Golds, but some people have reported it as not being payable in this scenario.

Basic and Flex fares run across fare buckets, there is no direct connection there.