I'm going to go against the grain here and say you can leave your dog 6 hours ...... Ime, it's only on mumsnet where you encounter so many rules!
You realise the people on MN are quoting from some of the biggest animal welfare organisations and rescues? Dogs trust, PDSA, RSPCA, etc.
Personally I think the occasional one off of 6hrs is ok with adult dogs but to expect that 5days per week is unfair. To expect it of a puppy is asking for trouble.
Also the "breed" you want is normally a puppy farmed pup or a byb who doesn't have a clue. It causes all kinds of health and temperament problems.
Even if you did find a well bred one, cockers are extremely energetic and need lots of walking for a dog of their size and I think are quite people oriented. Poodles are also extremely energetic and need a great deal of mental stimulation (they were bred as trick/performing dogs). So definitely not the crossbreed to spend 6hrs a day, 5 days per week at home without people.
If you do decide to go ahead, whilst being out 6hrs a day, 5 days a week, at least pick a less people oriented breed, that doesn't need lots of mental stimulation.
Oh and all dogs need walks out and about, no matter how much access to the garden they have.