If you can afford a soldering station then go for it. The benefit is they can be put in a standby mode which lengthens the life of the tips.Heat accelerates oxidation. But if you can't ,look for a minimum 60Wsoldering iron with a steel tip .Steel tips are copper inside, plated with stainless steel or iron so they last longer. Pure copper tips don't last as long and are more maintenance .
Stainless steel or Copper dish scrub pads will do in a pinch for a tip cleaner. Wet sponges are alright but if your not careful plastic ones can be a real pain for carboning up your tip. Natural sponge works a little better.
I use a small extra pot of flux to do a "hot dip" clean once in a while before a good re tinning.Do in a well ventilated area if your concerned about the smoke.
If your into it there are some interesting hot iron hacks on the internet to make them temperature controlled.
Using a variac isn't a very good idea because your just lowering the wattage of your iron when you lower the voltage so it just makes things worse.
I've not tried this myself but But apparently you can increase the tip wattage a little bit by wrapping copper wire around the tip base to make it thicker.So the tip holds it's temperature a little longer I guess.
Sometimes we need to do some unorthodox methods to get by.
Soldering tips are never plated with stainless steel, only with plain iron. Solder will not bond to stainless. On high quality tips, some areas will be additionally chromium plated to prevent solder from sticking there, so that it only ever wets the working area of the tip. Sometimes, only a very small area may be wetable (not chromium plated); I have a 'micro hoof' tip with a wetable area of less than 1 mm
2.
If you need extra thermal mass for bigger jobs, use a large chisel tip.
NEVER use plastic sponges for wiping a solder tip. Only use cellulose. Purpose made sponges are best and are not expensive, but kitchen sponges (of cellulose) work fine. Just make sure to rinse them
very very well, as they are usually sold dampened with glycerin or something which keeps them soft in the package. It is best to dampen the sponge with distilled water, since minerals and chlorine found in tap water are bad for the tip. Distilled water is cheap, so there is little excuse. Never "wet" the sponge, only "dampen" it. It should be just damp enough to be supple. If you first soak the sponge, then squeeze out as much water as possible, this is about the right dampness. It prevents the sponge from becoming scorched without thermally shocking the tip.
Periodically remove the tip from the heater element and clean both. Crud that builds up over time acts as an insulator. Inspect your tip to check that it has kept its shape. If the business end of the tip is deformed, then: you may be using excessive pressure on the tip, and/or the copper is erroded away under the plating. Over time one learns that the tip never needs to be pressed into the work, but only placed onto it. This is the single most important thing to both preserve tip life and prevent damage to pads on the PCB.
The best performing soldering irons dispense with the problematic heater-to-tip thermal interface entirely, and build the heater right into the replaceable tip. This makes tips quite a lot more expensive, but the performance is consistently excellent.