I spend the vast majority of my free time oil painting, with fine scale modeling being a much smaller portion of my free time. Turpenoid and gamsol are pretty comparable, though people will argue back and forth about which is better based on MSDS exposure specifications. Both of these are great choices, but someone that is especially sensitive to petroleum distilates may still have problems with these.
As for citrus based solvents, these leverage d-limonene as their primary ingredient, which is extracted from citrus peels via a steaming process, or a centrifugal process. d-limonene is still not something you want to pour over your cheerios, but it can be considered food safe, and is used in alternative medicine.
So, 100% d-limonene is pretty intense stuff, it will smell more orange than a bag of oranges, and it is supposed to be a bit stronger than turpentine. d-limonene does have a rapid evaporation rate, so it isn't really safer than spirits or turpentine in an enclosed studio. There is a company called Eco-House that makes a full strength d-limonene terpene, as well as a mild citrus thinner. The mild thinner is basically a smaller percentage of d-limonene, mixed with some other stuff, and is specifically marketed as a product for people sensitive to solvents. These aren't cheap, but they also aren't exactly expensive, especially when your health is a concern.
www.dickblick.com/.../eco-house-115-extra-mild-citrus-cleaner
*A note about using drying oils (linseed oil)*
So, some people recommended against using linseed oil as a medium for thinning paints, but drying oils in general are fine to use. Linseed oil, walnut oil, and if you are desperate safflower oil are great choices, and arguably better choices for thinning oil paint. The issue with using solvents to thin paints is that it reduces the oil/pigment ratio in your paint in such a way that you can have weaker paint films. This isn't going to be a problem most of the time, but it is something oil painters consider. Using a drying oil such as linseed oil is simply dilluting the paint by adding a higher percentage of binder/pigment. It will take longer to dry, but it results in a stronger paint film that doesn't risk interacting poorly with other layers of paint.
The least harmful route you could go would be to use a drying oil to thin your paints. Plan to experiment with it to get the effects you want though, as it will cause your paints to handle distinctly different than they do when thinned with a solvent.
The only time I thin my oil paints with purely solvent is when painting the initial layer of paint onto a canvas, when I am building up layers of paint afterwards I use a medium of either 50/50 stand oil/oms, or 30/70 stand oil/oms. Unnecessary info yes, but it provides context