Hi Sgk1289,
Welcome to the Mattress Forum! 
Just for clarity, I don’t make recommendations for stores unless they are a vetted member here of the site, but closest to Ambler you may wish to check out Mattress Unlimited in Montgomeryville, as they appear to have some Englander mattresses which may offer a good value, but their web site is incomplete and I would be sure to confirm the specifications of anything you might consider. I’m not personally familiar with this store.
Other than that, the closest would still be a bit of a drive to the east for you. Subject to first confirming that any retailer or manufacturer on the list that you wish to visit is completely transparent (see this article) and to making sure that any mattress you are considering meets the quality/value guidelines here … some of the better options or possibilities I’m aware of in and around the Trenton/Philadelphia/Wilmington area (including the King of Prussia area) are listed in post #4 here .
You can read a little more about Paramount (they make the Asteria for Bloomingdale’s) in post #2 here and the posts it links to. Unfortunately Paramount (or Bloomingdale’s) doesn’t disclose all the information you would need to know to make sure that there are no lower quality materials or weak links in their mattresses that could compromise the durability and useful life of their mattresses and if a retailer or a manufacturer you are dealing with either isn’t willing or able to tell you all the information about any mattress you are considering then I would avoid it because it would be a much too risky purchase.
Phoenix