There is no reason whatsoever that you need to shoot a static object from a tripod with 1/100s or 1/200s shutter speed. The shutter speed has nothing whatsoever to do with "soft focus": it just has to do with susceptibility to movements of camera and subject. Neither camera nor subject move; in fact, for shooting from a tripod you should disable image stabilisation as it is likely to do more damage than good.

Any shutter speed where the camera does not decide that long-term noise reduction starts being a good idea in order to counter variances in charge leakage on the sensor should be fine. On an older camera I have here, that's about 1/8s. That does not mean that results get worse fast as you go slower, it's just that they deteriorate.

You should avoid shutter press movement. Depending on the quality of your tripod and on sensor size and total exposure time, that may be a small issue, but using self-timer or a remote shutter release will make it a non-issue. Edit: using mirrorless myself, I forgot "mirror-lockup" mentioned elsewhere in a comment in order to avoid vibration from the mirror affecting the shot.

Your real problem is likely depth of field. The Canon 6D is a full-frame camera. For capturing a frame-occupying object that has depth commensurate to its width (namely isn't flat), I need to go F16 already on my 1.7 crop factor camera. On your camera, you'll need F22 or higher for the same feat. That comes with longer exposure times or higher ISO.

If significant post-processing is an option, depth of field can also be addressed by creating a focus stack, namely taking a number of photographs with different distances of the object in focus, and then using dedicated merging software for getting sharp focus throughout.

A reasonably current full-frame sensor should be able to go way beyond ISO100 before noise starts becoming an issue, and you probably are better off using somewhat higher ISO than doing everything via longer exposures since long exposures have their own problems (see above).

The obvious other remedy would be "more light". There is a reason studio photographers work with studio flashes and umbrellas, and in this particular use case, light boxes.