Ok. You will be inherently fragile. So that means you need two out of three of the following:
1. Lots of +hp gear. Hire a mercenary to help you get it. Use the item search on this site. Sandy cloaks for example are relatively gettable with rest.
2. A way to avoid being hit. If you focus on ac and use wands that help ac you can pull this off. Again, use the item search.
3. A route of escape. This means a recall potion, a teleport potion for when you are cursed and can't recall, but it also means being able to flee as needed. That means flight to avoid trip, as trip will keep you in a fight for a couple of rounds, and either enlarge to make bashes miss you more than usual or reduce to make giants unable to bash you (unless they reduce). Enlarge and reduce can be shop bought.

As you gain experience and judgement in cf (I mean you the player, not your characters) you can start to experiment with letting people try (or succeed) bashing and tripping you instead of making it impossible. You may land significantly more kills as they will be committed to a fight for a bit. A missed bash means no actions on their part for 3 rounds so you can blast them with 3 spells.

The above is all for low level fighting. It's a start. Try to exploit their vulnerabilities to various elements when you can. Also know that having the right elemental touch up tends to help spells of that element.