There is no safe ayahuasca dose, at least there should not be. If you want to play safe, go with shrooms or LSD. This is not meant to be an ePenis++ comment about 'huasca being for "real tryptamine thugs only", it's just that yage is what yage is and safe it isn't.
A more experienced sitter or co-tripper is of course a godsend because he/she can guide you and help you when things begin to get rough. Don't be too worried about titles like shaman this, apprentice that, things are not so stoic and serious as long as you remember always to respect the plant you want to use. After all, you are using something that is the plant's own to explore your mind. Doing that mechanically, disrespectfully, demanding an unforgettable experience, would be like waving a knife at someone on the street, saying "gimme dem moneys ho!"
If you can't find a more experienced person to help you, try finding a reliable trip buddy with whom you can share the experience. You may want time for your own thoughts during the dreams, but having two zoned out people exchanging experiences as they occur is a whole lot more comfortable than sitting alone in a room afraid that your body is going to die while you voyage through your mind.
The bed is an excellent idea, as is having a warm blanket nearby. A bucket for purging is just about a must, and a bottle of water so you can rinse your mouth with it and spit it in the bucket once you've drunk the brew is also good. Otherwise, go with what you feel is right, it's very hard to go wrong that way.
About the recipes, there are just about as many recipes as there are ayahuasqueros, and most of them work. My so far only dream was accomplished with the same plants that you have and the following extra ingredients:
3,5g syrian rue (more is okay, but I think over 5g is overkill)
10g mimosa hostilis
vinegar
spring water
The hostilis was simmered in about 3 dl water with little less than a tablespoon of vinegar added in for 30 minutes. Then it was poured through a cloth into another pot, so that the mimosa sludge stayed in the cloth and the water got through. Another 3dl water was put into the first pot, along with another measure of vinegar and the mimosa sludge for another simmer. The simmering/pouring was repeated three times. After that all the water in the second pot was allowed to simmer so that most of the liquid evaporated. Evaporating extra water from the brew is a good idea because it leaves you less of the foul stuff to drink.
The syrian rue was just crushed and boiled in 1dl of water for about 15 minutes.
Some people simmer the brew for more time, but I guess that's just personal preference. Allowing the stuff to sit in the fridge for a night before drinking might be a good idea though, because the little bits of mimosa that got through the cloth will settle down at the bottom of the brew. The sludge tastes awfu,l so the less you disturb it when you take the brew out of the fridge to be poured in whatever you want to drink it from the better.
