I agree, avoid mix and match! What if
you move your current two fronts to the rear-will that fit? Then get a new set of 3 for the front.
IF not, you don't have to get a C-V center channel. Could be a small C-V bookshelf speaker, sitting vertically, if you can live with how it looks. (This sideways layout typical of centers is terrible, don't get me started, that's a whole different thread!)