You can calculate the prescription you need for a distance using simple optical physics (inverse diopter is the focal plane in meters. E.g. if your prescription is -2, then uncorrected your focal plane will be 1/2 meters. If you use a +1.25 add (so wear a -0.75 net lens diopter), then your new focal plane is 1/1.25 meters). That would be a good start if you usually wear full-strength for close work.
It's said that -0.25 diopters is not noticeable by 50% of population, and especially for base prescriptions <= -2 ish the scale of distance quickly becomes negligible (e.g. a +1.25 add would give 31 inches and a +1.5 add is 26 inches, so only a 5" difference which is basically negligible. Also note that as one commenter noted, I've found my focusing ability changes throughout the day and also based on stress, sleep level etc., so that on a good day I might not need the glasses at all to see up to 32".
A final point is that if you end up going too weak you might find your posture being affected as you inch your neck forward to try to adjust. You could consciously try to prevent this, but I'm sure involuntary habits will kick in, so I think it's better to just choose a prescription precisely calculated for the focal length you want.
In principle the stressor explanation would hold for astigmatism as well, and you could try the same of reducing the cylindrical power as well. N=1 but I've found astigmatism is more easily corrected by the brain, such that you might not even need correction for a -1 cyl power whereas you'd definitely see blurriness at -1 sph.
