shaved for many years, mostly with a gillette (the 3 blade one, before the Fusion). took 2 blades to get through a whole head of hair, and yes i was a bit sore/rashy for the next day, but you'll be ok in a day or so.
protip: dont wash / shampoo first. the natural oils, grease and muck of your scalp are quite good at lubricating / protecting your skin; add shaving gel to the hair, HALF HEAD AT THE TIME, and as little water as you need. DO half head, then repeat.
(make sure to repeat, you'd look silly with half a head of hair)
Ofc, getting your GF to do this for you would be better.