Whats your budget? What mic(s) do you have?
Sounds like you would be recording one track at a time, so a single or dual input interface is more than adequate.
Budget is everything. If you have plenty to spend, I would recommend a separate A/D D/A converter and preamp - RME, Mytek, Benchmark, Lynx or similar converters (or perhaps Burl Audio if you wanna go the 500 series route). I believe they all make converters for as few as 2 inputs. Plus a quality preamp. That would be top end stuff.
A good quality, mid-range all-in-one solution would be something like the Focusrite ISA One, SPL GainStation or Universal Audio Apollo. They are both v. good quality preamps - I have an ISA although without the A/D card and it is a well made piece. A/D is likely to be more than decent enough aswell. Either the focusrite or UA are in the region of £400-500.
There is also the SPL Creon which comes in at a bit cheaper.
Lower range you'd be looking at Focusrite Scarlett, Clarett or similar. There are also a few companies doing small mixers which have onboard conversion; e.g Allen & Heath Zed series. Decent preamps for the price plus a few other nicities of mixers such as monitoring & headphone amps, rudimentary mixing facilities.
In your shoes, I would probably go for something like a UA Apollo if I could afford it. I'd take that over the ISA One as it has two inputs and you might want to do some stereo micing some day...
These are just a tiny drop in the ocean of options...so a budget would really help! Also think about what connection you need - USB, Firewire, Thunderbolt, Ethernet?
Finally...What mic are you plugging into it? If you are using an old dynamic or a Rode NT1A or some other cheap-ish mic, I would say dont bother upgrading your interface. Drop money into the mic first, it will make a much bigger difference.
