Plenty of vendors will build you a system. Fewer will answer the phone at 3am when it stops working. We do both, which tends to change how carefully the first part gets done.
Migration
We move workloads in stages with a rollback path at every step. No big-bang cutovers on a Friday night.
Operations
Monitoring with alerts tuned to real failure conditions, patching on a schedule, quarterly restore drills — because a backup you have never restored is a hypothesis, not a backup.
Cost
We review spend quarterly and tell you where you are overprovisioned, including when that means billing you less.