It sounds like you aren’t getting much leverage from the hoods. I have that issue on a bike I ride that’s a similar age.
My newer bikes, even the ones with rim brakes have a totally different lever design that allows a lot better braking from the hoods. It’s still best from the drops but is acceptable on the hoods.
Does your bike have integrated shifters and brake levers? Or do you have downtube or barend shifter?
If they’re not integrated, you can replace with a more modern style lever that’s a lot more comfortable on the hoods. I did this on a bike once, used relatively cheap Tektro levers and was pretty happy.
A higher quality cable and housing set can also help. Jag wire or Shimano are pretty good.
There are so many things I’d do, including selling and replacing with newer, before trying to convert this to discs.