I've found that first level survival is never a sure thing, but in my experience it's really the low hitpoints that make the difference. I don't like feeling like my players are only a hit away from death and I have to pull my punches-- a single lucky roll on a greataxe can spell doom for many 1st level PC's.
My solution has been to give 1st level characters HP as follows:
Roll 1dX+X+Y hp, where X is your class HD size and Y is your Con mod. Put another way, it's an extra 1 HD at 1st level. I don't think it will really hurt game balance long term, but in the short term until characters start to get their "sea legs" around level 4 it keeps me from worrying too much about killing someone outright due to a die fluke.
Thoughs?
Flat +6 hp for all PCs works for me.
My first level witch has 7 hit points, max of d6 plus one for a con of 13. He was hit with two crossbow bolts and nearly killed instantly. But he did survive. Our first level cleric was critted by an alligator bite and went from full health to -5 hit points, but survived as well, although we had to haul him back to camp and rest for a day since my witch does not have the healing hex and had not memorized a cure light for that day.
I once played a first level wizard with 1 hit point, back in 2e days. That's when zero hit points was death, not unconsciousness. He managed to survive a much more lethal version of the game than PathFinder.
I don't feel our characters are un-survivable, and their fragility does make us be much more careful in our encounters. I don't see a need to up the hit points beyond RAW. PCs die, and can die at any level. In general the room for error at level 1 is greater than at higher levels since the range from zero to dead is based on your con score for your entire career. At level 1 it takes a truly awesome blow to kill even a wounded character with a decent con score. At level 10 if you are down to your last few hit points, a single blow can easily surpass your con score. So in a sense I feel that first level characters are actually more survivable if you are fighting at low hit point levels.
We tend to use the XP for social interactions and such in the GMG. It seems to me (so purely opinion) by the time we are getting ready for second level we might only have 1 fight under our belt but have established ourselves within the "home community."
Obviously depending on the nature of the game this may not work worth a darn.
We do max hp at first level as well. Combat at first level is too flukey and it's worse when your Fighter only has 5 hp.
SJ