Personally, I'd convert to manual windows.
I had considered fitting electric windows to mine, but as most original motors are going to be at least 20 years old, and many pattern parts are unreliable, I decided to leave it as it was. I even had a problem with my drivers door manual window earlier in the year, but a complete door off ebay for £10, 15 mins of screwdriver and spanner work and the job was done.