with x(dy,mth,is_monday)
  as (
select dy,mth,
      case when datepart(dm,dy) = 2
          then 1 else 0
      end
from (
  select dateadd(day,1,dateadd(day,-day(getdate()),getdate())) dy,
      month(getdate()) mth
) tmp1
union all
select dateadd(day,1,dy),
      mth,
      case when datepart(dw,dateadd(day,1,dy)) = 2
          then 1 else 0
      end
  from x
where month(dateadd(day,1,dy)) = mth
)
select max(dy) last_monday
  from x
where is_monday = 1