Steppingin, how about a car harness if you only have a small boot? Bear in mind that car/travel crates don't need to be anywhere near as big as house crates, as you need the dog contained so they don't get flung around in the event of an accident.
hmc, I am so sorry you lost your Berner. We were supposed to be getting a Bernese when I noticed Oldgirl on a local rescue's website and couldn't just leave her there. We had researched breeders and were regularly emailing a couple about potential litters etc, but fate stepped in and we ended up with our gorgeous rescue girl instead.
I was/am very similar in terms of feeling guilty. We lost Oldgirl to osteosarcoma, very suddenly, last Spring and once we took on Pip I was wracked with guilt that we hadn't been doing anywhere near as much for Oldgirl as we did for him, but that's just the way it is, puppies are high needs for a relatively short while and eventually start to fit the family and settle within it's rhythms. That's why we choose to have dogs, because eventually they become part of the family and we start to compliment one and another. If they stayed as high-needs as tiny pups forever I am pretty sure less people would have dogs. People that want that level of constant activity choose high-energy breeds and do things like flyball and agility with them, most of us just want to end up with a well-rounded, easy going member of the family.
I am also pretty helicoptery when they're tiny, but as you are now doing, you have to try and make yourself remember that we want our dogs to enhance our lives, not take them over and if they do end up taking over they become a chore and that's not good for us or the dog. We all have to find the balance that works for us. Also, we need to teach them how to fit into our lives and if we start living our lives around them too much they never learn and become those well rounded family members.
I know needastrongone is very similar to us and put in 110% when she got her first pup, then found it all too much and no fun. She now has her second pup, is much more relaxed and loving it.
Re nipping, if shoving a toy in his mouth doesn't work, try getting your ds to stop whatever he's doing that's giving pup attention and turning his back. Nipping stops play immediately every time, even accidental toothy contact should be treated the same - the rule has to be no pup's teeth should ever touch human skin. If pup tries to jump and nip etc and is too much for ds, I'd recommend a short time out for the pup. No anger or scolding, just stop the game and lead him away to behind a dog gate or door for a couple of seconds. Then bring him back in calmly and get him to do something different, like a sit or down that you can reward.
A lot of it is age, consistency is the key and he will grow out of it as long as you always handle it in a firm, calm way. Lots of people on the New Puppy Mummy threads have had similar issues if you have time to do a search and read back through the posts and I think we've all come out the other side now with pups of 8/9 months old.