Whether you enter into a T&M type contract or fixed price depends more on the level of definition of the scope than it does to make a seller more profitable. T&M contracts are more suited in outsourced type services, where the contractors become more of an extension of the organization's employees, or where the scope and its requirements are vague and too ambiguous to nail down, i.e., the buyer is not totally clear on what it wants or needs at the time of project start. Under a T&M, the buyer owns the cost liability solely and, therefore, must manage costs in a very different way than on a cost plus or fixed fee contract. If you are a seller in that arrangement, you lose control over that in its entirety. If you feel you need a different skill set, more staff, less staff, whatever, too bad. Not your choice under this arrangement.
If your work is such that the scope is well defined and requirements are reasonably clear, a FFP contract can be a much better vehicle for you, i.e., you have more control and can be substantially profitable. If, as you wrote, you have trouble making a profit, it is not the type of contract that is the issue but rather your organization's estimating capability. Fix it.