Must be a mistake ... A one-category upgrade from a premier suite should be a Heritage Suite (formerly Shophouse Suite). The Heritage Suites are nice, but in the Shophouse wing just one or two floors above the lobby. While the rooms in the Shophouse wing are nice, they are all facing the Bugis Junction Mall or the Street with little natural light+mall noise or street noise, respectively. I would try to ask to be upgraded to an Executive Suite (which is the category above the Heritage Suite) or consider paying the difference.
Alternatively, as the premier suite is a nice an spacious room, you could ask to get charged only for a Heritage Room (1-category below premier suite).