Hi brass,
Not that it matters much but Simmons and Serta are now owned by Advent International (see here).
In addition to the TempurSealy International combination (which also owns Stearns & Foster) and Simmons and Serta being under common ownership the largest airbed manufacturer and 5th largest mattress manufacturer Select Comfort (aka Sleep Number) also bought Comfortaire the second largest airbed manufacturer.
There are other examples of multiple brand ownership in the top 15 or 20 mattress manufacturers as well such as Mattress Development Co being a Therapedic licensee and also owning Eastman House and Eclipse (see here) or the Kluft/Aireloom North American partnership with VI Spring.
Phoenix