Swapping is a lifestyle that once started is difficult to stop. You will need to think about the consequences very seriously. If you think it is a one off thing, it is not. You will keep experimenting and your husband will keep demanding that you experiment.
The most difficult stage is to get your wife to agree. It is a long process and you will need to find out the right couple/partner. This takes time and many meetings outside the home, till all 4 agree on the suitability of partners. It is easy for the man to have sex with a stranger, but requires some bonding for a woman to sleep with another man.
There are some dangerous pitfalls in this lifestyle. Jealousy is one of them. At some point, if you are all together, you may feel that your husband is paying more attention to his partner than to you. Or he may feel that you are moaning louder with his friend. This may create a rift when you are both having an argument and one of you brings up this topic.
STDs and HIV are a constant threat. You can never tell the safety as partners sleep with multiple partners. Use of condoms can help,, but still condoms tear and slip. Also the man may try to insert his penis without a condom and it may be too late for the woman to know when she is in the throes of passion.
There is often a tendency to cheat. Swapping may lead to one of you meeting your swap partner without the knowledge of your own partner. Recently we had a question where the wife keeps phoning her swap partner and the husband can do nothing about it, but regret what he has started as a past-time.
There are other ways to increase the intimacy between couples. Try sex toys. Try role playing. Sex can be great between partners, if they only fantasize aloud when making love. This way his fantasy will be fulfilled and you will reap the benefits of great sex.
Swapping does exist. One of the ways it is done is at a house party, all the car keys are dropped into a hat and then picked by the woman. The car key she draws, she spends the night with that partner. Swapping and swinging are common in major cities and you will find many Sites offering this Service. But finding the right couple/partner is a challenge, unless you want to sleep with anyone.
Whatever you decide, do not do it out of compulsion. And always insist on using a condom.