No need to worry about strength. Any action such as the defiance or big horn as mentioned above will be plenty strong for your needs. With the modern manufacturing techniques that small patch of metal missing in the bottom of the action compromises nothing. These actions are top notch. You mentioned this is going to be an ftr rifle, if so either one of these actions can support any length barrel you want to install. Presumably a rather long barrel for ftr? This is directly from big horns website. They do stress the strength factor.
The TL2 is a very stiff action, which has a closed top for stiffness. This makes an ejection port that does not allow for top loading, thus it must be fed from detachable AI magazines. An optional AW mag cut can be requested on the short action TL2 standard bolt face. The TL2 comes standard with the larger 8-40 threaded holes for attaching scope bases or one of our Picatinny rails. It also has a thick tang for stiffness that does set proud of most stocks. We have given up some on aesthetics here to have a stiff action. A trim tang may be requested if a person desires it. The built in .250 recoil lug gives a much longer barrel tenon and consequently more barrel engagement with the action for a sturdier connection. We feel this aids in accuracy when trying to support heavier barrels.
Not trying to persuade you away from getting a single shot action if that is what you truly desire, just know that a single shot action with a stock cut for a floor plate will be somewhat awkward.