Single glazed sashes might not be that bad in winter. No way a deal breaker imho and I think double-glazing is rather oversold. Some of ours appear to be original 1860's glass and we face the sea. Had them re-furbished such that any rotten wood replaced and the odd pane replaced and puttied, draft excluders fitted, new ropes/weights. that kind of thing and they're just fine in winter. Much cheaper than replacing them. Busy roads are going to be a lot quieter in 15 years.