It's seems like more up front, but in the long run getting the service done on the furnace by someone who knows what they are doing will be cheaper. Throwing parts at it replacing stuff that may or may not be the problem is not a good way of fixing anything. With an oil furnace you really should budget for a service every year, that said I'll try to help but some oil furnaces can be really fussy about proper settings. You said you checked the transformer, how did you check it? I ask because the tool to chek those is specific to oil furnaces and very expensive, some people check for spark by putting a screwdriver in between the springs but that really doesn't tell you if the transformer is weak only good or bad.
Now the points, or electrodes, they must be clean and regapped, the insulators must also be cleaned. They tend to build up with carbon and carbon can conduct electricity. For the gap, it changes with the nozzle size and spray pattern, for a general setting that should work for almost all residential set ups though, try 1/16 past the end of the nozzle 1/4 between the points and 1/2 inch above the center of the nozzle.
Take a look inside the tube that the nozzle assembly goes in, there should be a set of fins on the end of the tube, sometimes that piece cracks and falls off. Sometimes it gets plugged up with soot, if its covered in soot clean it.
Don't worry about fuel pressure, if you don't have enough you really should call a professional, messing with fuel pressure when you don't know what your doing will only cause more problems.
Clean the vent pipe and take a good look in the chimney and at the chimney cap on the roof if there is one.
Finelly and most important if there is a lot of fuel in the combustion chamber when it gets going again it can blow smoke and soot out of the front of the furnace. NEVER STAND IN FRONT OF IT WHEN RELIGHTING.
I hope this helps if you have any questions about anything just ask I'll do my best to answer. And as soon as you can afford it get a professional with a combustion analyzer out there it will pay for itself with less headaches warmer nights and less fuel consumption.
