I second the suggestion from 2010gmcyukon for Crutchfield as a source for aftermarket audio equipment.
Crutchfield has a built-in vehicle compatibility matrix, so if Crutchfield says that it is compatible with your vehicle, you can be confident that it will be. They can also help you out by letting you know what else you may need, like a steering wheel controls interface unit or a wiring plug set adapter, so that you get all of the required components that you need, in order to have a successful upgrade.
I would also recommend that you plan out your full audio system upgrade, component by component, as you don't have to upgrade everything at the same time. However, you want to make sure that what you upgrade on today's budget, will still/also be compatible with any future upgrades, when the future additional budget allows.
I have had great luck with Kenwood head units in a number of vehicles, including my 2007 Yukon XL Denali. Kenwood makes several head unit models at various price points.
Good luck on your audio system upgrade!