I am using the Tamron 90mm f/2.8 Di Macro lens Construction is plastic, AF is not particularly fast. However, optical quality is excellent, on par with the Canon 100mm macro. Price is a lot cheaper than the Canon. For macro work, the focus is done manually in almost all situations. 90mm at full extension (1:1 ratio) has the focus plane about 3 inches in front of the lens. At that magnification, the DOF is extremely thin, so aids that help get decent photos are:
1) Tripod,
2) focusing rail,
3) remote shutter release.
Some people can do macro shots without those, especially if chasing bugs around plants or on the ground, but it takes a lot of practice, skill and luck.
Using a fairly high shutter speed is almost necessary because all movements (camera and/or subject) are magnified with resulting blurring. And a high shutter speed, combined with a high f/stop (f/11 or f/16) for getting adequate DOF means that you need light, lots of it. So usually, I have a ETTL flash, on a bracket, connected via a hot-shoe extension cord, providing the light. Depending on the subject, I may have more than one flash arranged around the subject.
One of the ways you can work around the very thin DOF, is to use image stacking, in which a series of images is combined, with the software picking out the sharpest bits from each image, to produce a "synthesized" image containing mostly the sharp bits. For that to work, it really requires that the camera is kept perfectly still, and the plane of focus is adjusted by using a focusing rail. Adjusting the plane of focus using the focusing ring doesn't work well because that also changes the magnification. So in practice, you set the lens extension at the magnification you want to have, set the camera on the focusing rail at the nearest (or farthest) point, and then incrementally move the camera bit by bit, taking a photo at each position. It is not uncommon to have a stack of up to 200 images. Of course, this doesn't work if the subject moves, so it is really used only for dead (insects), inanimate, or very slow-moving subjects (like plants).
Edit: I don't know if the Tamron comes in a Sony mount, but being a third-party lens, I am fairly confident that it must.
Edit 2: yes, it does:
http://www.bhphotovideo.com/c/product/330645-USA/Tamron_AF272M700_SP_90mm_f_2_8_Di.html