i have a 12 ft pelican boat. It is abs plastic,am looking for ideas to make it more comfortable for my 13 yr old son and myself

WELCOME!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!

What do you mean by more comfortable ?

i have bad knees and sitting constantly bothers them, i am not sure if i raise the seats if it will be to unstable

You can either mount a piece of six inch thick High Density foam under the seat and raise the seat (pretty involved work) or just sit on the piece of six inch HD foam.  Or you ca sell it and get a canoe.  If you raise yourself too much, you are going to be at a much greater danger of tipping.  Also, make sure your stirrups at the front of the boat are correct for your leg lengths, you shouldn't be quite able to straighten your legs out, so you can push against them a little to stretch.

I dont see why you couldn't put a riser on the seat to make it a little taller.  I have a 9 foot pond prowler, that I can comfortably stand in and fish without feeling the slightest bit unstable.  I would love to see someone tip a pelican or pond prowler type of boat, I am not sure that is possible to tip one over, they are very stable boats.  

I was actually thinking of getting one of these type of seat: http://www.basspro.com/webapp/wcs/stores/servlet/SceneSevenDisplay?catalogId=10001&storeId=10151&langId=-1&productId=-7669&scene7Path=BassPro%2f52513%3flayer%3dcomp%26wid%3d500%26hei%3d500%26fmt%3djpeg%26qlt%3d100%2c0%26op_sharpen%3d0%26resMode%3dnorm%26op_usm%3d1.0%2c1.0%2c0.0%2c0&sourceName=images2%2f52500%2f52513.jpg&type=0&linkEnabled=false