A/C R12/R134 Conversion

[Malo83]

My A/C on my truck is still the R12 and it's been running great for the last 10 yrs but lately it's been slowly starting to loose efficiency, like when sitting at idle the air won't be as cold as when it's running at speed, which to me sounds like it's running low on R12, going to go looking around tomorrow for some R12 to charge up but everybody i've talked to says there is none available think i'll be good for the rest of the summer but thinking of switching over to 134 next year, my question is what is invoved in the conversion??? and done right???