Yes, you need a safeword or non-verbal equivalent for all kinds of BDSM play. It may be that you agree that when you say stop, the person stops. If you think you might say ‘stop’ or ‘no’ and not really mean it, then use a safeword that you wouldn’t normally say during play.
You can always use the traffic light system to check in during play. Green means you’re happy to continue, Amber/yellow means you need them to stop what they’re doing or change what they’re doing. Amber might involve stopping play for a moment to discuss what happens next or may indicate to the top that they need to change implement/area. That is something you need to decide between you before play. Red means immediate stop. Often it is the end of a scene and the beginning of aftercare.
During scenes where you’re unable to speak, if you’re using gags or are trying breathplay, you need a safeword alternative to communicate with the top. This can be a pattern of grunts, dropping something held in your hand or tapping the top. It’s essential that a bottom can communicate at all times.