Have you thought about hiring a kitchen design firm?
Many kitchen designers also do additions, as well as working with existing space to maximize usability. And we are trained to design kitchens.
For more information on kitchen designers see the National Kitchen and Bath Association (NKBA).
Many are also design/build firms, with cabinet showrooms, who offer complete planning and design services along with handling all the details of a new kitchen (one stop shopping).
There are also kitchen designers (like me) who just handle the design needs of the client (including additions). The client then hires a contractor to do the remodeling work and shops the products.
Whan one of my clients needs an architect. I tell them, and bring the appropriate person on board as a team member.
In my practice I recommend an architect if the addition is on the front, or a front-visible side, of the house. If the house is a historic structure. Or if the city building department has a requirement for an architect's stamp on the plans submitted for review.
I also recommend an architect if the project is going to encompass a lot, or all, of the structure.
It sounds to me as though your project is more limited in scale than that. So, unless your addition is visible in front and needs to conform architecturally with the rest of the home, you may be able to save the money you would spend on an architect and invest it in the products you buy for your remodel instead.