Check your programs too, e.g. do you need a hand wash cycle (I haven't had to hand wash anything for years), a sensitive/allergy wash, a quick wash for freshening up/emergencies, etc.
Do you sometimes want to open the door 30s into the cycle to add a missing sock? Some machines won't let you do this.
Do you want a time delay? And if so, do you want the time set to be to the start of the program, or to the end? The former is good if you want quiet until a set time, the latter if you want the wash to finish at a set time, e.g. when you get up or when you get home from work.
Do you want a time display for amount of time left? Do you want to be able to automatically do an extra rinse (e.g. if you have allergies) rather than have to run an extra cycle/rinse afterwards?
Some machines have options you can have in almost any combination, e.g. spin speed, temperature, prewash as you want. Others are pre-set, so, for example you can only have a prewash with a cotton wash but not with others.
If you are overwhelmed with choice, try Which? to choose a reliable brand (I think that they have a £1 trial? Quite pricey otherwise), otherwise John Lewis tend to stock Which-friendly/reliable brands.