Looking for Bar-end shifters (Shimano Golden Arrow)
Generally speaking, friction shifting works fine as long as you have the skill to shift, and that the shifter can pull enough cable to cover the whole width of movement needed.
Bar end shifters can be friction, indexed, or switchable between both.
Your existing derailleurs are probably fine to use with any friction shifter.
The linked Golden Arrow ones are quite vintage and will command a high price to find in decent condition.