What are you having trouble with specifically? Is the boss killing you or just getting through the trash?
The best thing to do is figure out if you are having trouble because the enemies are living too long or you aren't living long enough. If they take more than a few hits to kill, focus on your DPS stats as the faster the die the easier the situation becomes. If you are already killing enemies quickly, then bump up your defense stats a little to give yourself some more margin for error. Outside of that, pattern recognition of the mobs is your best friend.
I mainly focused on the melee DPS stats and slight armor for manor upgrades while ignoring mana and hp almost entirely for my regular playthrough. If you haven't unlocked the dragon class yet, I would avoid doing that so you don't get that into your class rotation right now.
Ninja edit: I should add that Assassin with crit upgrades is stupidly good so you could always grind that out.
I feel like that is the ONE downside in this game: if you upgrade everything simulatenously, you are really really handicapping yourself.
Monsters scale with your level which is simply every point you spent added together but if you put 10 points in everything instead of 20 points into a few selected things you scale like crap.
I really noticed that when unlocking classes before upgrading anything else and the game became harder and harder and harder.
So protip for beginners: everything into dps stats, only unlock the basic classes, then dump everything into attack, armor and health only when you feel you need it. Only unlock weight if you feel you need the new equipment though it's actually very cost effective in lvl gain vs stat gain. Forget magic. I could easily be 30 levels lower with the same stats for the paladin and just wreck the game but no, 10 points into magic points, 10 into magic damage, a point into everything to see where the skill tree goes etc etc
Slightly shoddy balancing imho.
And yeah, Hedgehogs curse is the reason I basically never pray.