Do I need to purchase boxspring with mattress?

You aren't REQUIRED to purchase a new box spring along with your mattress. But as someone said earlier, it will more than likely void your manufacturers warranty.

Most major manufacturers have this policy (i.e. Simmons, Sealy, Serta, Spring Air, Tempurpedic, Stearns & Foster, etc.)

So really it just comes down to how important keeping your warranty intact is to you.

Bunk beds generally use pretty low-grade mattresses. The mattresses that are more comfortable, have more support, and last longer generally are taller than the safety rails on the bunk bed so you cannot use them,

You do not have to purchase a boxspring or foundation with your mattress. Just know that the manufacturer reserves the right to deny a warranty claim when you do not purchase his mattress with the specified and coordinating base support.

Learn What is a Boxspring and What Does it Really Do?

http://www.stlbeds.com/articles/2008/05/07/what-is...

Sometimes you need to purchase a boxspring to keep a warranty. If you aren't worried about that, then you probably don't need a new boxspring. I know Sam's Club sells mattresses separate, if you have a local Sam's Club.

Forget about all of that and purchase your son a memory foam mattress. Memory foam mattresses have dropped significantly in price (due to the significant increase in competition) so you can purchase a quality unit for under $500 (a good company that produces a low cost memory foam mattress is Overnight Mattress -- http://www.overnightmattress.com)./

Memory foam is the most supportive and comfortable sleep surface available. It aligns the spine and eliminates pressure points. This means no more tossing and turning, no more pain in the morning and no more snoring. Your son will get the best sleep he's ever had and he will feel much better each day because of it.

They usually are for just mattresses, if you use the box springs it will be really high to climb into.You can use what they call a hollywood frame, in your case it would be 2 twin size as a king bed 2 twin box springs .Then you could buy just a headboard for the frames.

if the box spring is in good shape it recommended but you don't have to

No the salesman is just trying to get you to buy another thing from him.