Merida bicycles are not sold in the USA (at least where I live in California) so I'm not sure exactly what yours looks like. Anyway, I'd suggest just getting a similar 10 speed cassette to what you have now, but with a 32 tooth big ring, and see how that works. It should be a simple swap as most Shimano RDs can be used with the larger 32-tooth cassette ring; you might have to buy a new RD, but try just the cassette swap first. Changing to a 11-speed cassette might create problems with indexed shifters, which could cost you more if you have to buy new shifters/brifters and a new RD.