There are local furniture stores in the residential enclaves.
If you go to say Shaukeiwan or Mongkok, same mattress, different prices (post discounts) due to rental, overhead differences. So, I would take the mtr and go to the one with less rents.
Local furniture stores are mom and pop shops that sell from Dining Rm to Bedroom items.
Pricerite is the most convenient, not sure if they sell Airland. Just ask them.
Have also heard of Ulfenbo too.
Read More On their website, there is a page for mattresses. Their prices on general furniture is pretty low. I love their shoecabinets, a must have in HK. Their shoecabinets are so practical, and are also carried in WingOn. Mine did, but costs less at shinway.com.