Good for you, I really do think this is the right decision for you, and even more so, for your dog.
I am sure he will not be in rescue for long and they will ensure that he is placed in home that can meet his needs in terms of exercise, training and activity. It will take him a little while to adapt, but dogs live in the moment and I am sure he will soon settle down. In fact I am sure he will get used to the new regime faster than you will
As has been said, he may well spend some time in a cocker savvy foster home where his temperament and needs can be properly assessed.
I have never been in this situation thank goodness, but I know I would find it difficult to come to terms with. However, you will have done the best thing FOR HIM by recognising that at the moment you are not able to give him the sort of home he needs , despite the pain it will cause you
That makes you a good and caring owner - never let anyone else make you feel otherwise.
I hope your friends and family will be supportive of your decision and help you come to terms with it in time. Please do not beat yourself up about this - sometimes it just does not work out no matter how much you want it to, but just imagine how you would cope with this situation if it continues - not good for your doggy friend either. Now, he is young enough to adapt and learn to have a different routine that will better suit his needs and activity levels
Stay strong. Sending hugs from here