Don't do this.
You need to talk to your husband if your sex life is unsatisfying. It may be something you can work through if you communicate about it. It is possible you can use toys together, get a babysitter in to spend more time together just the two of you, a weekend away... Or maybe you've grown apart and the relationship needs to end.
ONSs can be fun, but if you need an emotional connection, they probably won't be. People in ONSs are usually there for their own pleasure, so you need to be fairly selfish about taking your pleasure - but if I'm having a good time, then usually the other person is too. It has amazed me how few men ask about contraception or insist on wearing a condom - most will not mention it at all until I do.
Swinging or an open relationship can work, but again, it depends on the person and how much emotional connection you need. It needs a lot of communication, honesty and trust with your current partner, and to keep checking in to see how it is going, because how you think it will be is almost definitely not how it will be in reality. Again, it's definitely not something that works for everyone.
Whatever you decide to do, don't lie. I'm quite a fan of a ONS, but I'm single. I do not knowingly go with men who aren't, and the couple of times I've found out they weren't, it pissed me off - I'm not willingly getting involved with a couple, and particularly not if one of them is unaware, and I don't appreciate being forced into that because a guy failed to mention he had a wife or girlfriend already. (I suppose there could be others who have succeeded in covering up an existing relationship, but I don't feel resentful because I don't know; I would be pissed off if I found out, but as I'm not going to see them again, it's unlikely.)
Just don't go behind your husband's back. Talk to him. If you can't work out how to improve things between the two of you - do it if he agrees willingly - that does not mean you coerce him into it in any way. Or break up and then do it.