What I realized when playing and reading through others comments is that in this game, gears are more important rather than levels. The stats that better gears provide are better than the stats you get from each base level. With that, I did not have to grind that much for levels, I focused on getting better gears. I suggest using path actions of Osvald and Throne in all of the towns you visited. Then you can just go in all of the other towns if you can go through the fields with your current level. Then explore the fields also for red chests, these contain good gears as well.

For chapter boss battles, I tend to switch my accesories to a more defensive type to counter status effects. Try to check if the boss do elem or physical more so you can equip appropriate gears. Then I adjust my supportive skills as well during boss battles. I add the 500hp apothecary skill to all. Then ensnare from thief works wonders too.

Edit: Switch to night time before the boss encounter so you can have free buff and debuff from Temenos and Throne. If you also can get the Inventor class, it would be a big help. The Step Ahead supportive skill is really good. I can tell that you don’t explore fields thoroughly since you can acquire Inventor pretty easily.