I've only just seen this so don't know if my reply is too late. I stayed at the Greenwich Premier Inn recently and was very happy with it.
The family rooms were clean and beds were fine. There were two single beds and a kingsize. Some Premier Inns I've stayed in before had a double sofa bed instead of the two singles which wasn't so good.
The PI is just round the corner from Deptford Bridge DLR station, only about 3 minutes walk, so trains into central London are easy.
I'd definitely stay in this Premier Inn again. Hope that helps!