We are very permissive with our 14-month-old and always have been. We let her have supervised play with typically "dangerous" things (ie, she loves to play with our D&D dice, which are choking hazards), but there are always rules. The biggest rule that we started around 6 months was "NO MOUTH". She learned pretty fast that if she was being allowed to play with something special (like the dice, or the TV remote) but put it anywhere near her mouth, she'd get told off and the thing would get taken away.
Obviously, it's not a perfect system because kids need repeated lessons to learn. So there were times of frustration and power struggle, when she'd defy us by putting the thing in her mouth and then holler when we took it away. But we stuck to our guns on the command, in part because we knew we were being so permissive otherwise that we felt entitled to be really strong on the few rules that were there.
It has paid off. Last night, she spent half an hour playing with my dice (supervised closely), and not once did she put them near her mouth, because she knew playtime would be over if she did.
Also, I have a rule in my head because of something I remember from childhood that pissed me off...I used to HATE it when I asked why I couldn't do something and the answer would be "because we said so." That's a BS answer. I have a personal rule to never, ever say that. If I tell my daughter she can't do something, I ALWAYS give her the reason. I will say, "Peo, if you put the remote in your mouth it will get sticky and might not work anymore," or "Peo, if you bang on the glass like that it could break, which would be very dangerous for you and ruin the cabinet. So please don't do that."
Even when I have to be really harsh (by which I mean taking her aside and speaking in the Angry Mummy voice, which I reserve for serious situations so it always gets taken seriously), I always take time to explain why I'm angry. I'll say, "I've told you four times now not to hit me with your toy. It hurts me when you do that. I don't like being hurt, and I know you're a nice girl who doesn't want to hurt me. It's not safe to play like that. Stop it now or I'm taking the toy away."
She'll pout, maybe glare at me a little, but she'll stop, at least for awhile.
So you really can be permissive but stick to the main ground rules. Think of the rules you do have as being a solid foundation for allowing the rest of the freedom. Explain the reason for the rule each time, even if the kid doesn't get it, because one day they will get it and if you've been consistent, it helps them learn and avoids them being able to nitpick you back.
Incidentally, you sound like a very sensible person. You sound like the kind of person I'd get along with really well, and that's rare for me to say online. :)