i have been using mono tippits which were easier for me to match to my flies working off diameter as a newbie .

with the smaller flies 16 down the breaking strain is getting a little sus with mono so have decided to go for a copolymer whreby i can use the same diameters i have now which are turning my flies over nicely but give me added breaking strain.

i was thinking of a range from 0.14 through 0.20 which will give me enough variation to turn all my fly sizes over (12-18's)

my copoly leaders have a 0.20 tip ..

do these diameters sound ok ???

Took the same journey myself. From my experience the range you suggest sounds ok. I tried copolymer and fluoro to get over the same fear and had to faff about a bit to get turnover right. The biggest wake up call though was knots and knot strength; I had to change the mono habits of a life time from other types of fishing after losing flies and fish when I started using copol. You've fished enough to know this; but there's loads of advice on here covering the do's and dont's.