Looking for exactly the same thing.... What did you go with in the end...?

The advice above is right because very few manufacturers make a double oven now so there is not much choice and they don’t seem to have controls or handles that line up. I think that you have a few options- you could stack the microwave and the double oven in a tower which is likely to be the cheapest- again the double oven may not match the compact appliance. You could have your microwave built under the counter somewhere else in the kitchen so that they don’t have to match. You could have a standard single oven and by the side a 45cm appliance with a warming drawer. Or you could have two side by side 60cm ovens with two 45cm appliances. Don’t forget that your appliances both 45cm and 60cm can be conventional or steam ovens or microwaves or grills or do more than one function. Or they could be sous vide ovens or coffee machines. Look at the Siemens website for inspiration and have a think about how often you need the various functions- for example you might decide you use a microwave so rarely that a cheap counter top model in the utility room would do and you fill the kitchen space with another full sized oven that gets used more. Alternatively you might add a single oven in a less convenient position for the rare occasions it is used- again this could be the utility room.

There are plenty of double ovens on the market. I rarely use my top oven for cooking, only for grilling bits and bobs, but mainly toast. To be honest I could manage without it but just like the thought of it being there as a back up. Warming drawers are expensive. We fitted 2 a couple of months ago for a customer (one in each housing under the ovens) and her reason for choosing them was that she didn't like microwaves. Whether or not she has used them, I don't know. They're not something I would personally cough up for. I guess it depends on how many you're cooking for on special occasions that you feel leads you to want the double oven. I cook for 8 most Christmas days and manage fine in the bottom part of my double oven. The turkey is cooked before everything else goes in and I have 3 shelves Personally I do not like to see an integrated microwave installed oven a double oven. It's too high.

@Sarah L, yes this is the bracket. We have it but the joiner is just unsure. We went back to IKEA and it is used in some of the installations. We'll have to have another conversation. Thanks so much for taking the time to get back to me.