how'd you get magic resistance, the furthest ive ever got is to the bottom level of the mines to get killed by the dorf king (was low on hp when i got to him). on may occasions ive been hit by a sleep trap and been killed in the mines but never a polymorph.
The easiest would be to play a wizard... all wizards start with a cloak of magic resistance.
Or you can find a bone pile of a former wizard.
Other sources include randomly generated cloak of MR, gray dragon scale [mail], and quite a few artifacts grant MR when carried.
Note that while only MR can save you from a polymorph trap, many troublesome attacks (e.g. werecreature bites and wands) in the early stage does not require MR - just reflection and good MC (magic cancellation).
MC is for special attacks that much touch you to take effect - like werecreature's bite, footrice's petrify attack, poison stings from insects. You can get MC from many cloaks, mithril armor, etc.
ran two characters yesterday neither made it to the mines, one never got past level 1 because i couldnt find the down stairs so after searching loads and running out of food i retired him.
Sometimes there are items generated on top of the stairs - move boulders and statues, and pay attention when you walk onto a square with items. If there's a stairs, you get a message for it.
Sometimes stairs are hidden in sections that has no access except a diagonal move, which you are most of the time carrying too much to use. You will need to find a pick axe or wand of digging for those.
Or you can simply dig downwards! You will be dropped a random number of levels down, so immediately seek the up stairs for the way back. You will need to leash all your pets if you want them to drop downwards with you.