Kitbashing in Scale 1

Morning Gents,

I have started scale 1 modelling with a Marklin set (55033) I got from my wife as a birthday present. I would like to extend my rolling stock with some kitbashed wagons. I was visiting model shows in the UK and looking around in the net, finally I ended up buying a Tenmille Mink A wagon kit. This is more like an experience to see how to build something from scratch.

Next would be a kitbashed wagon. I would like to build a continental model that would match in dimension with my other Marklin stock. I am thinking about a simple 2 axle gondola for the start. I would prefer to by the main frame, axle guards, buffers from a kit, and just build on top of it from styrene.
I don't have a workshop, just some basic tools and a dining table to work on. This is why I prefer to use plastic for the top of the wagon and use kits for parts (such as wheel, axle guards, etc.).

I know that Tenmille has wagon kits that I can use as a base, but what other manufacturers would you recommend? Is there any commercial product for scale 1 motorized bogies? Where would you recommend to buy plastic products in the UK (sheets, beams, etc.)?