I had the same problem and my son hated nasal aspirators. Then I found the Nosefrida, a Swedish aspirator, mentioned in a blog. I ordered it (even paid overnight shipping - I was desperate!) and I love it! The link is http://www.nosefrida.com/.
I have to warn you - the concept seems really gross, but it works so well. I've told several of my mom friends about it, and they now sing its praises, too. My son still flinches a bit (probably a gut reaction from being poked with the aspirator for so many months!) but it's much easier on both of us and gets so much more mucus out. It gives him such relief. Definitely do saline drops as others suggested and then use the Nosefrida if his mucus is more on the thick side.
Good luck! I really hope the Nosefrida works out for you! :)