i have a ritchey torque key .. that seems to work well enough for seat posts, stems etc
I have a 1/4" drive torque wrench made by Teng Tools, which I originally bought for the smallest fasteners on my motorbike.
It has a range of 5 - 25Nm, which should do the the trick I think. It also has a degree dial on the head for "torque-to-yield" applications, which seem more common these days.
Edit: That Ritchey Torque Key looks a nice bit of kit, depending on whether you think you need a wrench for other bike applications or not.
I use a Park Tool torque wrench that is bike specific and cost 80 bucks on the internet....a lot of bike mechanics use this particular brand and model which ranges from 3-25 Nm....it was a good investment
BBB brand which starts from 2NM. about $80 from cell.
I will suggest that home use id a different environment than industrial or commercial workshop use.
So the tool is less likely to need regular calibration.
You wont get "close enough" by feel. People generally tend to overestimate the required tightness by a fair bit it seems, especially at low torque values. 5Nm doesn't feel very tight at all.
FWIW my Teng torque wrenches all came with individual calibration certificates, so that barring accidents or abuse I feel I can be pretty confident in their accuracy.
i bought a 'zero' kit from lifecycles in norwood. seems good. and has all the hex bits that most bikes have on them. plus it's a 1/4in drive, so suitable for any other sockets/driver adaptors that are sold in hardware/automotive stores. it does 3-15nm, so not quite the range of some of the other tools mentioned. but it is easily locally sourced.
I have a "Pro" (Shimano), works very well, easy to use. The things with torque wrenches is that they cost about $80-$100, you only use them a few times a year, but when you need them - you need them. Dont dare not use one when it comes to carbon. If its just for your seat post I'd suggest you borrow one from a mate or just get the bike shop to adjust (I wouldnt think theywould charge you just to tighten one bolt).