Bosses can be tricky while solo but for the most part you should be able to defeat them. For bosses with no adds I would never use bombard.

1. Pre buff with Rally and Grim Focus (whatever Morph) and debuff Boss with Mark

2. Snipe and hold down heavy attack, stop cast half way so it goes through but then

3. Poison injection- at that point Snipe, HA and Poison injection will all hit almost at the same time

4. From there I'd probably Cloak ----Ambush----Surprise Attack

5. After that depending on the mechanics of the boss use a combo of Cloak, Double Take or Mirage and potions

6. A lot of bosses are predictable and have an advanced attack you can avoid. Use this to get distance and some DD from safety of range while kiting then back in with cloak---ambush----Surprise Attack and #5.

Some of the stuff I wrote can be tweaked but if I remember this is what I did running 2H/Bow Stam (I've been magicka now that I am Vet).