I could be flippant and say that the 444/544 is not an easy car to see out of anyway, but that wouldnt be constructive or help you.

Most of the Volvo accessory brochures of the period, show the "Lucas" style mirror previously mentioned. What Volvo sold wasn't Lucas but a variation on the theme.
They generally showed a door mounted mirror, mounted on the flat area just below the vent window.

My P210 came with fender mounted mirrors, mounted rather far forward on both fenders. I found them useless. I have a door mounted mirror on the driver side currently, that works but really needs to have a longer arm. The P210 body tapers outward and a mirror with a bigger head and longer arm would be more helpful. I think also the passenger side mirror would have to be mounted very carefully should you choose a door mounted mirror for that side, so that it is high enough and that the vent window support doesn't get in the way of what you see.

One of the later style 140 mirrors would give you a bigger mirror head, but may not stick out far enough off the body to be effective. I guess you'll just have to try it.

Another possibility is to pick up a copy of Street Rodder magazine. There are frequently mirrors available in that market that could look neat on a PV, since they are intended for vehicles of the same basic design time period.

Good luck.
Bob Tescione