Most couples have a short list of things one of them is curious about and has never raised, usually because the raising feels riskier than the thing itself.
Introduce it outside the bedroom
Suggesting something new mid-way puts your partner on the spot with no time to think. The same suggestion over coffee is a conversation instead of a demand.
Agree how you stop before you start
Knowing there is an easy exit is what makes people willing to try things. This is not bureaucracy, it is what makes yes possible.
Expect the first attempt to be awkward
It usually is. Laughing is fine. Treating a clumsy first go as a verdict on the whole idea is what stops couples trying anything twice.
Debrief lightly
A short "would you do that again?" the next day is worth more than an hour of analysis immediately afterwards.