I'm 64 on Thursday and due to medical issues I've lost 150 lbs and much of my muscle. So, the downsizing issue is a current thing for me. I tried to carry my MF Bronica ETRS kit to shoot the hospital and decided in quick fashion the kit had to be emptied. I first decided on a single lens, then dumped the metered prism and speedgrip for the WL finder and a handheld meter. Only the back on the camera and a couple of rolls of flm instead of multiple preloaded backs. In stripped trim, it works but still heavier than I'd like as towards the end of the day it becomes heavy.
Then compared it to the Rolleiflex T and the T is much lighter. It needs a cla so I've not used it but it obviously is a realistic and practical alternative.
Found a Asahi S1a with a couple of lenses and thought maybe a well built 35mm slr would work. This model does not have a built in meter so it with the handheld was taken out for a dry run for a day to see if too heavy. It weighs more then the Rollei and less than the Bronica in stripped form. No go, better than the Bronica but still was too tiring to carry for 8 hours. Frustrating to say the least. But all is not lost for me as there is the Leica CL with the 40 and 90mm lenses. As i do not use the 90mm as much as I probably should, I left it home and afte 8 hours I did not feel the camera at all so, it is my standard today. Someone suggested I again try an M6 but the heft ain't light and not a whole lot lighter than the Asahi so the M series is out but the earlier Barnacks ar smaller and lighter and could be a good compromise.
Also have a Canon AF35 (first model) that is plastic, fully automatic and has auto advance and AF. Noisy as heck but the glass is very decent. It weighs almost nothing compared even to the CL so it was considered by not ready to downsize quite that much. Lastly, the 1/2 frame Konica. Auto everything and thin. Easily slips into a shirt pocket and not much thinker or heavier than many of those small digitals that only have a lcd screen. I've yet to load it but used it for some years and surprisingly good. Plus 2x the number of exposures per 35mm cassette. It will be probably the last film camera I carry as it is so small and light. Until then, the Leica CL with the 40mm will do the job. I will keep the T but suspect it will remain a shelf queen as the Leica is smaller and lighter.
I do have a dslr (yuck) but it is heavy so, my son who has claimed possession can keep it.