Any 5w40 will be fine. With regards a specific brand, you won't go far wrong with OEM Elf, however a lot of people prefer other brands - it's just down to personal choices. If you contact our site trader @oilman of Opie Oils, he will be able to recommend something for you, and also any offers that they have on at the moment.
Loads of posts on this, some recommend OEM, some say a decent branded one (shell, motul, fuchs etc). Think as long as you're not buying it from poundland you'll be fine!
If you don't regularly do an oil change minimum yearly then the engine will only be knocking on heavens door earlier. It'll also ruin resale value in time
For the price and ease of doing an oil change there is no excuse no matter how many miles you do a year. If you DIY just keep receipts for oil and parts and record the mileage.