I've found that on taildragger landing gears that anywhere from straight to 2 to 3 degrees of toe in helps. The big thing is to avoid any toe out. Also ensure that the legs are stiff enough to avoid flexing in ways that the angle changes. Flexing up and down is fine. You just don't want the gear to flex fore and aft to any great degree. So if you're using a single piece of music wire then it has to be quite large to be stiff enough. A double leg that forms a "V" shape from the fuselage to the wheel axle does a lot for avoiding any fore and aft flexing which alters the angle. Or using aluminium landing gear legs.
In the end though nothing you can do to the landing gear will totally avoid the model going sideways. We simply have to learn to spot when it's starting and be ready with the rudder to catch it before it gets too far. This is especially true on grass strips where clumps of grass can catch at one side or the other.
The other factor is to always take off and land directly into the wind wherever possible. With tail draggers this is especially important. If your flying field does not allow for this sort of 360 degree freedom then you need to sharpen up those rudder skills to allow you to take off and land with cross winds. Which is something you just have to do anyway since, as I said before, it is just simply not possible to just put the power to the model and get a straight takeoff with any model. They will all respond to torque, runway roughness or slipperiness and cross winds.
The only way to provide a rudder free takeoff would be to set up a rail that the model rides along during takeoffs.