What will make our house smell nice?

[Birdly]

This is a particularly pertinent question at the moment, as DD and DS have both just had big sick/poo illnesses!
Should I go for pot pourri, candles, oils, gel things? And what fragrances? I like lavender and geranium but haven't managed to find anything that makes the fragrance linger.

Thanks all for your ideas - will gradually work my way through the lot of them! (Am particularly looking forward to the cake smell and bread smell! )