If you're mounting it on a hard top, then you can use a standard screw socket and then just screw a basking bulb in. Using one with a built in reflector like a BR30/BR40 or a PAR38 will work and not require a dome to redirect light. If you're using a mesh top, you could just sit a dome fixture on top of the mesh or suspend it above that using an adjustable stand - that gives you the ability to adjust heat output by raising/lowering the bulb vs using a dimmer or dimming thermostat on a fixed basking bulb.