Should I shave my dog or not?

When we got my maltese, my mom and I were a little careless and didn't take it seriously that they need to be brushed OFTEN. and so he ended up getting mats all over him...and for a while we were working hard to brush them out and try to cut them out but there were just so many, and more would appear and they started meshing together...and i don't really notice it anymore, we just got used to it, but whenever i give him a bath i see all the mats and it's just not good...my dad thinks we need to just shave him and get a fresh start but i'm not so sure (and my mom will need a LOT of convincing). So my two questions: one, would a dog groomer actually groom all the mats out for us? then we wouldn't need to shave him. and two: when should we shave him, if we do? my dad thinks summer because then he won't get cold and he'll be less vulnerable to fleas, but i think he'd get really sunburned in the summer, i heard that happens to dogs like him. but i don't want him to get too cold...what time of year is best?