Gazza
My tap tds is 96ppm, I run 2 - 11Ltr DI vessels with Tulsion resin from DAQUA. I have a 400ltr van mount & top up from customer outside taps if & when needed (no water meters in scotland)
Tulsion resin is the best IMO, I've tried & tested loads in the 6 years I've been using it. Dowex MB50 is a very close second.
Tulsion resin from DAQUA is 72.50 per 25ltr bag all in (delivered next day)
I use TWO bags per year, so my pure water costs are £145 per year. That's purifying on demand with no RO involved.
Hope that helps.