There is a persistent myth that over exposure is required to get good shadow detail. This is not necessarily true and entirely dependant of subject contrast range. AA is known primarily as landscape photographer where very often he has bright clouds and dark shadows in the images and where the subject contrast range is great. Result is that he uses a 10 zone system and to make a 10 stop subject from black to white fit onto a negative which then fits directly to paper, you need to overexpose and reduce development from manufacturers recommended times.
So what are manufacturers recommended times based on? Well, usually around a 7 stop range for negative films. That is based on the "average subject" brightness range and not high contrast scenes.
So now take your subject and find out what its range is. You have a spot meter so that should be easy to determine. Since it is indoors I strongly suspect it will be a low contrast subject. Very probably less than 7 stops from black to white unless you have windows or shafts of sunlight coming into the image. For a 7 stop or less subject range you should not be giving additional exposure so expose at ISO speed and use manufacturers recommended times. That will give you the contrast in the negative which will fit the paper.
If you are still getting low contrast negatives, then increase development time 30% and try again and if you are still getting low contrast negatives, then go to ISO 60 or above.
As you know the zone system as says there are zones 0 thru 10. By default each of those zones is 1 stop of exposure. However, the zone system is so flexible that if you have a subject of say only 6 stop range from black to white, then you can say each zone is 1/10 of that range. That would make each zone step 0.6 stops. That means that if you meter what you want on zone 3, then you would reduce exposure by 1.2 stops or 1 1/3 which is close enough. This assumes you have tailored development of your film to fit a 6 stop range.
The same applies for slide film except slide film is high contrast film and out of the box it accepts only 5 to 6 stops brightness range from black to white. Assume 5 stops and therefore you can say each zone is 1/2 stop step. So if you meter what you want on zone 8 then you open up 1 1/2 stops to expose it correctly. A little trial and error is required but that will be pretty close.
So to recap, high contrast scenes need extra exposure and reduced development from manufacturers recommendations (based on a manuafcturers 7 stop range).
Normal contrast scenes require use of manufacturers recommended numbers and low contrast scenes require reduced exposure and increased development.
But all of these require knowing how long to develop for.
For b+W films you should do some print tests:
To calibrate for a 10 stop subject range. Expose an even subject at zone 1 and then the same at zone 9 using 1 stop for each zone step. Print the zone 1 neg until it is just slightly less dark than a max black. Then print the zone 9 neg using the same print time and it should have just a hint of grey.
If its white then reduce development a little (20%) and try again. Iterate until you nail it.
To calibrate for a 7 stop subject range. Repeat the above except make each zone a 0.7 stop step. So exposing for zone 1 would be metered value and then closed down 4 x 0.7 = 2.8 stops ( a little over exposure is best so make it 2.66 stops. i.e. 2/ 2/3). Then expose a zone 9 neg which will be plus 4 x 0.7 from metered value. or rounding up for a little over exposure makes that + 3 stops. And print as above.
To calibrate for a 5 stop subject range. Repeat the above except make each zone a 0.5 stop step. So exposing for zone 1 would be metered value and then closed down 4 x 0.5 = 2 stops. Then expose a zone 9 neg which will be plus 4 x 0.5 = 2 stops from metered value. And print as above to prove development is correct.
Note that a zone 1 neg should have a small amount of density greater than the fb+fog. If the zone 1 neg is same as fb+fog then you need extra exposure (reduce film speed). If zone 1 neg is too dense then less exposure is required (increase film speed).