The DM will probably say you're just another wight...
In the core rules, wights can gain class levels after becoming wights, but wights don't keep class levels they previously possessed. That is, in core there's no template for wights that permits wights to maintain their classes. In the core rules, killing yourself by gaining one or more negative levels from the feat Death Devotion means transformation into just another (fairly smart, quite charming) wight, which, given the wight's lack of a Level Adjustment, the game's designers thought was inappropriate for a player-character.
...Unless other sources are allowed
The Dragon #300 article "The Risen Dead" details a wight template (75-6), giving the template a Level Adjustment of +4. A sidebar details how the article's various undead can come about using the spells create undead et al., the implication being that just getting snuffed via energy drain is insufficient for templated wightness, but the whole thing's a pretty big if anyway, so it doesn't hurt to ask the DM. The template is also available in Savage Species (136-7) with a few alterations (no claws, for instance). Andy Collins (he of the dnd-3e to dnd-3.5e transition) has a similar template on his Web page, but that template omits any Level Adjustment.
Libris Mortis puts the the Monster Manual wight as having a Level Adjustment of +4 (32) and, in case you want to play a wight from level 1, presents the undead monster class wight (40). The book also explains that a creature that suffers level loss and subsequent death at the hands of an undead creature that can spawn an undead rises as a its previous class -1 level / spawn monster class level 1; such a new undead creature continues taking spawn monster levels until the monster class is completed then the creature can take more of its monster class levels then character levels.
Finally, Savage Species also presents the 3-level prestige class emancipated spawn (75-7), which allows a spawned creature whose creator dies and that lost its special abilities from transformation into an undead creature to regain those abilities.