I'd second the m/l recommendation.
We had mediums for Cole originally but eventually he grew out of the rise of them but still needed the skinniness (is that a word?!) of the medium's waist so we went for medium longs.
They still fit him well now, aged 17 months almost. I wouldn't go for mediums as they won't last so long, particularly if you prefer higher rises on nappies.
I'm selling some medium/longs if you want to try one first before buying new.