Remember that SET DATEFIRST will recompile your code. And also, not everyone has DATEFIRST 1 as default setting.

Try this code that is safe and doesn't rely on any setting and also, if doesn't have the annoying time portion.

SELECTGETDATE() AS Today,

DATEADD(DAY, DATEDIFF(DAY, '19000101', GETDATE()) / 7 * 7, '19000108') AS NextMonday,

DATEADD(DAY, DATEDIFF(DAY, '19000101', GETDATE()) / 7 * 7, '19000115') AS MondayAfterNext