Most people recommend trying a chin strap before deciding that a full face mask is necessary. Another thing that some have been successful with is training their tongue to seal their mouth off from their airway. Just keeping the mouth closed is generally not enough to prevent mouth leaking although it will prevent mouth breathing.
I would try a chin strap first if you like the nasal pillows. Chin straps, however, seem to be as individual as masks, so the first try may not be the optimum. There is one that many seem to like best by Carefusion but I can not keep it on my head.
Ii use a full face mask and it works well for me but it took some effort to get to that point.
Try the Respironics premium chin strap. I dont use it now because I got the tongue seal trick learned finally. But once on it aint going anywhere. Its wide but comfortable. Tried a couple others that either wouldnt stay on or didnt put my jaw in the right position so still lip leaked. Ehhh I got no front teeth so not hard to lip leak LOL.
The Respironics premium pulls straight up on your jaw not slightly back like other chin straps I had. If there is one thatll stop your mouth leaking that one will do it. Not pricey either and lasts forever.
Sorry I should have added that I do have a chin strap, BreatheWear HALO. It definitely eliminated the mouth breathing but does little to stop the air escaping past my lips.