Thanks guys, unfortunately as per above, there's not even any reward seats available for the route I want, even economy.
I may still check 3 days out for any Qatar reward seats if any (probably almost 0% chance but I'll still check regardless).
I'm very keen to change due to the seat map for our BA flight in PE being already almost all pre allocated - we're either going to be stuck in the middle 2 seats in the middle 4 seat section, or sitting apart in aisle seats (on opposite sides of the cabin).
BA is hopeless / ridiculous in wanting to charge AUD$100+ just to allocate seats!