It is often the first sentence that is hardest. Here are a few ways to start, depending on how you usually talk to each other:
Curious: 'I have been thinking about trying a sex toy together. What do you think about that?'
Concrete: 'I read about a vibrator you use during sex. Do you want to have a look at it with me?'
Inviting: 'Is there anything you have wanted to try but not said? I have something I would like to suggest.'
Playful: 'I have an idea for Friday, but you only get to find out what it is if you want to.'
What they all have in common is that they leave room for an answer. Avoid phrasing that sounds like a problem to be solved, for example 'we need to spice things up' or 'I do not always come'. That may be true, but it is a different conversation – and that conversation becomes easier once sex toys are already something you can talk about in a relaxed way.