Not necessarily a zoom lens but a tele to start with.
The budget solutions out there to "double" the 200 (=400 mm) have their shortcomings. The biggest is the temptation to just add another lens (a longer one) and nothing else (like a monopod or tripod - or just throwing some time at the new hobby to practice instead of buying more stuff and then be disappointed (again?).
If you throw significant money at what you you have just recently perceived as an additional desire for your photography (like a G lens) you might actually be interested in sharpening your skills along. Just trying w/o commitment will get you nowhere.
Check out this link:
That will be you in the end. Wait until the new Tamron 70-300 comes out in A Mount. Use that time to practice with your 55-200, practice how to shoot sharp pics at 200 mm (hard enough already) then get the Tamron at least. or look for a second hand 400 mm tele (and find out about the cost of really good glass on the way). Prepare for the price and weight of the Sony 70-400 G. That was my final decision after doing it all wrong along the way over 20 years:
That is a pretty easy one to answer. All of the modern Tamron lenses, say within the last five years, represent great VFM. IQ is generally excellent, build is pretty good IMO and the price is a fraction of the Sony equivalents. Tamron also tend to be cheaper than Sigma.
