Well, I've been using nappies for 26 years now. My dds all walked long before their first birthdays despite wearing the old fashioned terry squares, the same type of terry squares my mum used on me, and they didn't hold me back. Nonsense to say wearing cloth nappies hold babies back from walking.
Ds2 is nearly 7 months old and has been sitting up well since he was 20 weeks - maybe his cloth nappies gave him something to balance on
To be honest, most of the nappies I use are not much bulkier than disposables anyway.
Tonight he has on a disposable for bed, because I have been ill for a couple of days and haven't got round to washing his wraps for his night nappies. Dh has commented about the chemical smell from his nappy within half an hour of him having it on. Dh wasn't particularly keen for me to use real nappies, but he's converted now.
I also find that disposable nappies are nowhere near as good at containment of explosive poo as cloth! Takes much longer to change a whole outfit after one of those accidents than just changing a cloth nappy and putting it in a bag until home time.