Hi @Ruth1971 and welcome
The most efficient dryers use heat pump technology similar to an air conditioner or dehumidifier so check for that. These will have much less of an impact on the environment and your pocket. They are more expensive to buy unfortunately but the Smeg you mention is probably on the expensive side and might be one of these, if it's reasonably recent.
Conventional condenser dryers are pretty much similar to vented types in terms of energy consumption. Check out the energy rating, the difference in consumption can be quite staggering.
From experience I'd search out reviews relating to the specific model of washer/dryer combo that you are being offered because the drying functionality of some of them makes things quite difficult in a larger family using cloth nappies. Some models can only dry half the weight that you washed and do so more slowly than a stand alone dryer.
We use the washing line as much as possible. I think our clothes feel much nicer when dried that way. The sun also has some great benefits when drying nappies (have read of some of the many topics about it on here). Even so there are times when it's too cold/damp, we use a separate dryer during those times.
