First of all, I'd like to say sorry that your original question has been hijacked by the smacking vs not-smacking debate. I feel partly responsible because Kittywits threw down the gauntlet & I picked it up.
As far as your worries go, I think that there is no simple answer.
I am a single mum of two children. My ex-H bailed out when my DD was 14 months & DS was 3yrs 7 months. DS went from being a happy, normal 3 year old into a child possessed by the devil. If I had smacked him for seriously bad behaviour, he would have been a walking welt & I would have had repetitative strain injury. I was at my wits end, I spent the whole day telling him off & his behaviour was getting worse & worse & worse.
I ended up in a child psychologists office & very slowly we started the long climb out of the pit of despair to where we are today.
I did lots of things. First of all I tried to work out where the day fell apart the worst. Secondly, I thought of how I was going to tackle the bad behaviour (sanctions). Thirdly, I looked at ways I could start being more positive towards DS. Fourthly, I put a structure in place for each day. Fifthly, I worked out a consistent bedtime routine. Sixthly, I thought out meal & snack times better. Seventhly, I worked out ways in which DS could get more exercise. Eighthly, I thought about me.
That is just a brief outline of all the things I put into place to help us get back on track. I could go into each point in loads more detail & there are lots of other small things I did too.
If you feel anything I have may be of use, please feel free to ask me more. Once again sorry about your original thread.