The washing machine reviews on our site allow filtering by capacity, so you can easily identify which of the larger ones we’ve reviewed perform the best. And yes, we try and test the most popular appliances, which means more focus on the typical capacity washing machines, these days around 8kg is average, but we have looked at several larger machines over the years so we should have plenty of results that will be of interest to you.
Regarding stacking, it will most likely be easier to stack the same brand washer and dryer as many manufacturers make stacking kits to keep everything secured, but that’s not to say that you have to. As an earlier commenter suggested, using a rubber stacking mat (available from appliance retailers, or you can make your own) will help reduce vibrations and improve grip, so your dryer’s less likely to move about and fall off.
If you are stacking, you’ll need to have the dryer on top of the washing machine, not the other way around - washing machines are more prone to vibration and movement than dryers, so putting the washer on top is a risky proposition.
If you’ve got a vented dryer you could also consider wall mounting it, which will be a safer option again.