Aye, new boiler is on the cards for next year. Was planning to stick with a regulare boiler though (WB 18ri or Viessmann compact) as I like the relative simplicity.
Yes, that's the way I would go. System boilers are fine, but I prefer to keep boilers as simple as possible. Also, if you're a diyer who likes to maintain his own heating system, you have access to most items if the PRV, pump and exp. vessel are seperate to the boiler. The only advantage to your situation is space, because you mention that you have a small property.
I have a closed system with a Remeha Avanta heat-only boiler in my own house.