I know it is frustrating. This life-rearranging aspect is why a lot of people choose to get older dogs rather than puppies! It is a great deal of work. The puppy DOES require a rearranging of life and home. No doubt about it!
We have an open plan home, too. Since we added Willow to our home, we have returned to using the xpen when we are not home. Both Cedar and Willow go into the xpen like you describe Daisy going into her crate, but it gives them extra room. Plus they can be together and play a bit.
We generally leave our xpen up during the regular day so it is convenient, but when people come over, we fold it up and set it aside. Most people never even know it's there.
We also have a room that has a 7 ft opening that is separate from the main open plan. When Cedar was about Daisy's age, she had access to the main floor EXCEPT for this one room. It is carpeted (rest of house isnt) and it was out of sight. So of course when she wanted to poo inside, this room was her destination.
To limit her access to the main floor but NOT this room, we used two chairs and a fitted bedsheet to block it off. We spread the bedsheet taunt between the two chairs (the seat part was on the inside of the room, so Cedar couldnt jump up and over). It was easy to unhook or step over for people, but it was still effective keeping Cedar out. Plus, you can pick a sheet that you feel is more visually appealing (and you can always remove it when someone comes over, etc.).
Keep up the effort. 6 months is the time when the pups start to test you. They are like 14 year old kids--they think they are ready for more independence and give signs of being ready, but most parents know they are still too young to be completely autonomous.
Cedar (tri), Willow (blen), Holly (ruby), & Bella (blen)