It all depends on what you are soloing and where. There used to be a problem with dungeons that didnt have Tome books. This has now been fixed by their introduction. Its a case of how quick you can kill verses how fast you die. What you have merited also plays a part. Regen, Refresh and Reraises from books helps. If I sub a mage job its usually the fasts low mp expending spell I have to make the wyvern cure me. I usually solo sam for the TP feed and the quicker death to the mobs. This means you dont need to heal yourself as much because you have already killed the mobs. Ultimately its up to your playing style which route you go. There are plenty of solo options with books and food.