Best respirator

Use a water based finish and skip the respirator.

Any industrial store will have a wide selection. Find one that is comfortable and seals to your face and use organic vapor cartridges. 3M makes good ones bu there are many other OSHA rated respirators.

As a former HazMat team member, let me say that the whole topic of respiratory protection is mind-boggling. The task of matching mask against vapor is far more complex than you'd ever expect. Here's a link to a 3M "Respirator Selection Guide" - it's 124 pages, if that'll give you an idea.

So the simplest solution is going to be switching to water-based solutions like Adrian suggested, and also getting good ventilation.

If you've gotta go with VOC solvents, etc, the very best thing to do is consult an Industrial Hygienist. The nut of it is matching specific chemical hazards to specific chemical protection - if the bad stuff is also in the air you're breathing. A relatively expensive but totally effective alternative is BYOA - use SCBA tanks & masks, or even (not recommended but you get the gist) SCUBA gear.

Don't gamble with your lungs.

Sundstrom Safety Silicone Half Mask Respirator Available at homedepot $32.97

The SR 100 half mask Air Purifying Respirator is intended for use when maximum safety and breathing comfort are required. The heat-treated silicone material is FDA and BGA approved offering a safe and comfortable fit that molds to the shape of your face. Extremely low breathing resistance makes this mask optimal for low to strenuous work activates.

A unique face seal design providing a high protection factor Also available in small/medium, filters and cartridges are not included Cupped face seal accommodating various face shapes and sizesdouble exhalation valve design providing only half the breathing resistance of competitive respiratorscan be used with our P100 filter and / or a range of chemical cartridges which can be "piggy-backed" together Face piece is made of heat treated silicone with minimal risk of contact allergiesplastic components are made of high quality nylon plastic Easily adjustable V-shaped elastic head harness with a large crown platelatex free quick and easy donning and doffing procedure Meets and exceeds NIOSH standards for air purifying respirators Machine washable at 104 degrees F