I usually do my flat barbell benching in a smith machine (I have no spotter), and last week for the first time in a long time I got on a real bench and was shaking with half the weight. So should I start using Dumbells until my stablizer muscles are good and then move onto the flat barbell bench? or should I just go ahead on the flat barbell bench and deal with the shakes till i get used to it?

Personally, I would stick to flat benching and develop your stabilizing muscles in that regard.

After your flat bench training cycle (6 - 8 weeks), switch to db work and keep the results coming.