If you suggest swinging out of the blue, she’s likely to think she’s not enough and become insecure, especially if you’ve not having much sex together.
Variety isn’t a bad thing. Most people crave novelty especially in a long term relationship. I’d be inclined to open a conversation about how you both feel currently, and whether she thinks sex has become a bit routine. Ask questions of her. Would she like to change anything? What would make her feel more desirable?
You might want to suggest Killing Kittens. There’s lot of resources there about intimacy and desire. Everything from masssge to lap dancing to BDSM. That might be a good way to start talking about spicing things up generally before you get on to parties. The pre-party chats are a good way to meet people beforehand and she could connect with other women attending,
If you do decide to look into parties, please be aware that there’s a great deal of variation out there. A room of 3 couples fucking surrounded by 20 wanking single men might be a bit much for a first timer. Ideally you want to find a venue with a relaxed, no pressure environment with clear rules on consent and no “wanking dead” wandering about.
DP and I started out with a very clear boundary that we just played together as a couple at parties, it was a turn watching and being watched. Then we progressed to soft swaps then full swaps in the same room. These days, he happily waves me off on solo dates. The key is to go slowly and agree your boundaries.