Blanes to Barcelona - an overnight hotel in central Barcelona?

First post ...My sister and I will be in Blanes in mid September and want a one or two (2/3 star) stay in Barcelona reasonably close to La Rambla. Any suggestions? My sister has some walking difficulties - a hotel with lift is necessary and I  from looking on line today that prices aren't cheap for our likely date/s especially as September is festival time. I realise that Barcelona prices will reflect the demand, but hope to find somewhere centrally located that is clean and comfy and no too noisy! Thanks - pleased to have stumbled across this forum as I'm sure I'll have lots more questions - due back in Blanes in July for the fireworks.