If you've never tried it before, 45mg would be a good jumping off point, just to determine your body's unique reaction to this particular type of hypnotic benzo; benzodiazepines come in so many different flavors, and I personally have quite a dysphoric reaction to both Lorazepam and Clonazepam, but enjoy the other seven I've tried.
I donno, I personally like to get a decent 'taste' of a drug before initially bombing myself so that when I do take higher (and in the case of temazepam more enjoyable) doses I'm able to appreciate the subtleties of that particular benzo flavor - The elements that it shares with select other benzos, and the subjective qualities that make it my favorite of the benzodiazepines.
I FINALLY found what I was looking for in the benzo realm with temazepam, and I definitely second (or fifth, or whatever) the comments suggesting that ~60mg will make you feel really great. I'm just saying that for me, I can more fully enjoy it after properly prepping myself. Either way, enjoy it man - to me, the feeling I achieve is about as close to the euphoria and sense of cozy well-being of opiates that I've experienced (to a slightly lesser extent, triazolam [Halcion] but it's halflife is so short it's not enjoyable for too long).
To sum up my ramblings I would start with 45mg to get a feel and then definitely hit 60mg for a benzo experience that dwarfs that of the Lorazepam you've been familiar with.
~ vaya