Email marketing questions on complaint rate

I'm building my own list with getresponse using single opt-in, and according to some intros you have to stay under 0.1% to be on the safe side, but it looks very hard for me to keep it under 0.1%(mine is always around 0.13%) with single opt-ins, most of the time my mails only provide good infos and don't even promote anything. Although it's not a big list right now, I still don't want to lose it and it's growing every day, so my question is, what's an acceptable complaint rate for single opt-in lists? And what should I do to lower complaint rate except switching to double opt-in?

Thanks