The main is issue is light as you seem to understand. There are two ways to get around it:

• High ISO which all modern DSLRs do. Most cropped-sensor models perform very closely, so the real question is if you can afford to go full-frame which is more expensive and more heavy. Otherwise among cropped-sensor DSLRs, the difference in high-ISO between an entry-level and advanced model is actually quite small.
• Bright apertures is a property of the lens. This is where things get costly quickly. Since people do not tend to move much in conferences, you can go with a set of prime lenses with F/2 or larger maximum apertures. Something like a 35mm, 50mm, 85mm and 100mm for APS-C DSLR. The weights adds up obviously, so the other option which lets you react quickly is a 24-70mm F/2.8 or 17-55mm F/2.8 if you need wider field of view. These work really well in low light.

Ideally you should get both. Bright lenses have the advantage of focusing faster too because they let more light in. You can go one stop down with a 24-120mm F/4 or similar. It has more range and does not dim as much as most bundled lenses which go down to F/5.6 at the long end.

So the answer is that any DSLR can do and leave a good budget for your lens. If you pay more for the camera you will generally get better autofocus speed but it is probably not needed in a conference environment when you can predict where people will be easily.