I just went in my first mine last night in my current (light) playghrough, wearing Fenris armor and fighting with an iron buckler and black metal knife!

It wasn't easy, and I got piled on a couple of times, but it shouldn't be easy. I wouldn't go in without bonemass ability and over 250 health, and I always know the way out in case I see a situation coming that I don't want to deal with, which happened a couple of times.

In my case, I had to retreat to the entrance a couple of times to both have an easy path to the exit and to limit their ability to pile on. I've found that a knife is very effective against a seeker, even a 1*, but taking on two or more at once didn't work nearly as well.

The knockback in the game currently is crazy, especially with seekers. With a knife you have to get combos in. it just doesn't work if you're constantly getting pounded and knocked back. It's a similar problem with a sword, but the sword can hit and stagger multiple enemies, and I don't remember the knockback being as bad with heavier armor.

Anyways, just take it slow and careful, and know when to run for the exit.