I think we can all be guilty of anthromorphism from time to time and tend to think too much about what WE need rather than the dog. Generally speaking I find that dogs that are left at home while their owers are at work seem to be much more biddable and attentive when it comes to training and also get a lot more out of it. The key to a successful partnership with your dog is the energy you invest in the time you do spend together rather than the amount of time (Quality over Quantity).
If you look at any pack of wild dogs/wolves they spend the vast majority of their day laying around and sleeping with only short periods of intense activity, dogs aren't actually meant to be 'on the go' all the time. I have border collies and working cockers, both breeds were obviously designed and bred to be working dogs and as such they would spend their time kennelled/tethered until such time they were taken out and trained/worked. I can't see that many gamekeepers/shepherds fretting over their dogs 'quality time' each day and to be honest I'm pretty sure the dogs wouldn't either.
I would love to be able to spend all day/every day devoted to my dogs but unfortunately I have to work to keep them fed, pay vets bills and be able to afford our agility classes/shows/flyball tournaments at the weekends etc etc. As it is, both I and them greatly appreciate the time we do spend together and always make the most of it and they're all eagerly waiting by the door to load up into the van every morning, knowing they're coming to work with me and will be in their crates until their lunchtime walk...are they bothered by that??? Not one bit!
Caroline, you've proven that your system can work already with your exisiting dog so I don't see any reason why another wouldn't fit in just as well. I don't have any experience at all of show bred cockers so I don't know if there's any difference but I have found my workers (and others I've met) to be very easy going about everything and quietly accepting of whatever routine you want to introduce them to. (I think they may just be the happiest dogs I've ever owned lol). I would suggest you construct a puppy pen somewhere in your home where you can leave the pup with toys/chews etc and have someone come in during the day to let the pup out and spend a bit of time with it, it would also have the company of your other dog. I do this with all my pups and my mum pops in to see them during the day's I can't get home and they've all turned out just fine!
Good luck in whatever you choose.