If OP wants to have a single seat (presumably the main reason to choose Polaris over EU carriers) and a decent soft product that hasn't been downgraded under the guise of Covid hygiene theater, then LX is a good option. If they're flying the 77W, then all single seats are "throne" seats, and therefore cost $100-200 for advanced selection or can be selected for free at T-48h (slightly ahead of OLCI). If they're flying a 333/343, there are throne seats on one side, which are chargeable per the above, and there are non-throne single seats that alternate between being closer to the window and closer to the aisle, a subset of which can be selected for free.