Hi, I understand your want for the beauty of candles and to some degree the love of fragrance we have come to enjoy in the world. However, for myself and possibly your husband it may be the burning of the wick that actually causes the sensitivity. The fragrance is the 'gasoline' for me, whether it be from a plug-in or candle. I can somewhat tolerate a no fragrance candle if used with caution.
I just wanted to share my experience.

Aroma Naturals makes a Plug In Air Freshener made with pure essential oils.
Each includes heating unit and all natural essential oil. Adjustable strength for any size room. Plugs into standard 120v outlet and leaves one outlet free. Refills available. You would have to see what scents he can tolerate.
www.aromathyme.com

I do not know of any plug-in but Vermont Soy Way Out Wax makes a candle and air spray that does not seem to bother anyone with allergies. The product is "Clean Air" in both the candle and air spray. It comes in a neutral scent plus scented.
Hope this helps-
Ann

Sorry to be so blunt, but air fresheners in the home are just nasty. I have heard the "but I have dogs" excuse many times. I have 2 dogs and have always had 2 dogs for many years that spend most of their time in the house. To keep your house from smelling doggy, bathe the dogs, vacuum often. I have never had a doggy smell in my house. I have a friend who has dogs and air fresheners, but her house just smells like lemony dogs. Bleck!

The Vermont Way Out Wax "Clean Air" Products are not air fresheners-but odor absorbers. They absorb the odors-not mask them.

Many use them in their homes to absorb odors that someone may be allergic or sensitive to. Others use them while cooking to absorb food odors. They also have products for pets.

The industry's advertising concept is to get people to "cover up" smells and replace them with their synthetic fragranced product. This obscures the need to CLEAN what is unsanitary and deadens our sense of smell to natural fragrances( clean linens don't smell of Tide/Downy etc, they smell of linen; a clean man doesn't smell of product X, he has his own signature smell, as unique as his fingerprint).

People who use these products a lot become used to the smell and need more to "feel good" Some products also are designed to deaden the sense of smell so that you need to use more. It can be an unintended addiction.

All synthetic fragrances cause restriction and irritation of the lungs. They are a big part of indoor air pollution, which is much worse than the outdoor air.

People who have already been injured by these chemicals, such as those with MCS, "allergies", "asthma" will have a difficult time being in a house that has become saturated with toxic fragrance chemicals.

I suggest a return to a clean house (bake it out as Debra recommends) where people (such as your husband) are more important than the things companies persuade you to buy.