To each their own of course, and you have different tyres to mine, but you might find 1.7 bar gives you a better compromise between feel and ride. 1.9 bar would, I think, give a fairly harsh ride.
I agree that the car does feel squirmy with the factory recommended 1.5 bar.
Regarding steering: if it feels a bit weird you may need to get toe-in and camber checked. There are several opinions on what this should be on a 4 wheeled Morgan. I have had two knowledgeable people suggest 0º toe-in, and one suggest 0º camber and the other 1º camber.
If I recall correctly toe in should be an overall 1/16 inch, I set up my plus 8 with this and .75 degrees of negative camber which worked well. Nice positive turn in, and no steering wheel shimmy induced.
