We use Arkwrights Beef Dry Dog Food, which is a complete food and marketed to ‘working dogs’ like our sofa surfer. You can get a 15kg bag on Amazon for a tenner: https://www.amazon.co.uk/dp/B003TL23FM/ref=cm_sw_r_cp_api_i_LAd-Ab399S139
Our local retired greyhound trust, where we adopted our dog, feeds Arkwrights to all their greyhounds so we bought two bags of it when we adopted him. He’s never had any issues so we never saw a need to change to a different dog food.
In April, we started giving him a spoonful of porridge in the morning mixed into his breakfast and and since then his stool has also been more solid (it wasn’t why we started giving him porridge, and his stool wasn’t too bad before the porridge, but it was a welcome side effect for when the poop bags have to come out on walks). We measure one heaped spoon of oats and let it soak in boiled water shortly before breakfast, takes no time to prepare. Don’t know exactly what your dog is going through but you might consider trying it for a week and seeing if it helps.