Did you make sure to find all potions of strength and scrolls of upgrade? There’s 2 potions of strength and 3 scrolls of upgrade on the 4 levels before each boss. These enable you to equip items you otherwise wouldn’t be able to to equip. Scrolls of upgrade lower the strength requirement of an item. Alchemy with a potion of strength produces a potion that lowers the strength requirement of an item by two, but which can only be used once per item. One strategy can be to hold off on upgrading until you have an item worthy of it (tier 3 or better, better if it’s already upgraded) which you have the ability to upgrade so that you can use it. Avoid upgrading low-level weapons and armor unless necessary.

Potions aren’t 100% random. For certain loot room there’s guaranteed to be a corresponding potion to solve it, for example if there’s a room with items behind magical fire there will be a potion of frost somewhere in that level. One enemy in each region is guaranteed to drop potions of healing, in the first area for example this is the flies.

Regarding bosses, one strategy can be to make sure you have a strong enough character right before facing it. This may mean that you will need to upgrade low-level items anyway. With time you’ll get a feeling of how strong you need to be for a certain boss and region, while still enabling you to progress in the long term.

Also make sure to get to know the abilities of your class, subclass and magical armor and use them to your advantage.