I did the same dd awhile back and ended up with:

https://www.autoglym.com/products/exterior/snow-foams-pressure-washers.html

Start with Polar Blast, then Polar Wash and then onto Polar Seal.

Good results - not sure if better than others but thus far I have been happy with the results.

Karcher do their own attachment (just a bottle and nozzle that fit onto the end of your standard lance, or you can get a standard (non-branded) lance with bottle that fit the Karcher model you have - the nice thing is that Karcher run a standard attachment, unlike a few others (Stilh being one)

All the regular places sell them - https://amzn.eu/d/aZzOlra - and the non-branded are usually £5-10 cheaper.