Mobil 1 high mileage oil

[Heaveho]

I have an elderly Lexus IS300 Sportcross, which has, as they are prone to do as the mileage increases, begun to use oil. Having consulted with the dealer at the last service, it was agreed to go from 5/30 to 5/40, but it's made little difference. For the first time in it's life it's about to have an oil change at home rather than at the dealer, reason being that they want £31 per litre for oil that I want to keep in the car as a top up.

I've decided to change the oil and filter and use something I can buy off the shelf at sensible money so I'm not getting ripped off every time I need to add a splash. Anyone have any experience of the Mobil?