Walking boots are one of those items you have to go and try on as different manufacturers have different last shapes so what works well for one person will be awful for another. For example from personal experience, Meindl tend to be pretty wide, and Asolo a little narrow with a pretty tight heel cup You also need to be comfortable with things like flex and weight.
Also very important to match the boot with what you intend doing. No point in buying light weight fabric boots if you are going scrambling in Scotland in the winter.
Find somewhere local with a good selection that has a stone practice walking ramp and go midweek when they are quiet so you get someone really knowledgeable with plenty of time