I’m happy to hear your little guy is feeling better. Heart failure is always a tough one, and usually is one of those that takes people by surprise. It sounds like he got the right care and your vet’s a keeper.
Do remember that no one will think you did the wrong thing when/if you need to make a decision. I’m an ER tech, and deal with more euthanasias on a weekly (heck, daily) basis than either regular daytime vets or even the shelter I work for. I’ve had to make the decision for two of my own, too, and I’m a firm believer in too early rather than too late. I see the “too late” decisions and aftermath all the time, and it’s no favor to the pet for sure.
It sounds like you’re truly in the right headspace for when decision time comes around, considering you were already thinking you may need to do it soon. Buying time is good, and the meds your little dude is on will probably give him many, many more good days! If you have a chance to have a specialist do a cardiac ultrasound, do it. He/she will be able to determine whether different doses or different meds will help more than what your dog is already on, and will be able to tell you exactly what’s causing the heart enlargement, and give a more definitive prognosis. Those are always helpful to know when you see your guy start to have trouble again. If you know it’s something that won’t be helped by different meds or higher doses, it will help you make a decision even if it’s another year from now.
Best to your family and your doggie!