Need help with my muffler?

Ok so i want to buy an aftermarket muffler. The length of my stock muffler inlet to the tip of the exhaust is 32 inches. the mufflers i am looking into are like 16-20 inches. so with that said. i would need an extension or the muffler would be way under the car. so i was wondering if i could buy a pipe to match the inlet (2.5 inches) then just put that between where i cut my stock muffler off and put my new one on? is that possible? and my other question is. do i need to have it welded on? or could i just clamp it on. like, clamp the extension pipe onto my exhaust pipes and then my muffler onto the extension pipe. would that be possible? or would i need to weld it? its just such a pain, because i need this extension pipe because all of the mufflers are too short and wont even end near the rear bumper. so if anyone with information about this please help me it would be greatly appreciated.