After looking at a number of the software/online offerings and either finding their cost too great or their functionality too basic I've reverted to a spreadsheet. It's still a bit more basic than I'd like but at least the data is there if I want to do something with it.
I have a main table of the individual animals (one per row) that stores record number, status (current, reference, removed), flock and individual animal names, flock number and individual number (combined = the tag number), breed tag number, group name/colour (management identifiers), gender and sex, castration date. breed, number of horns, date of birth and current age (calculated), birth type, sire, dam, date acquired, time in flock (calculated), date of removal and reason for removal (sale, death, slaughter).
This is brought together using a pivot table to create an individual animal sheet that self-populates, including a several generation pedigree, to show all the pertinent information about one sheep once I select the animal from the slicer.
I have a further sheet, populated using look ups once I enter the individual tag number (the digits after the zeros), int which I enter any weight and condition score data I gather. I have set up a pivot table to pull this together from which I have a graph that plots each individual animal's weight over time. The slicer allows me to filter the graph for any of the management groups I have set up or just look at selected individuals.
Aside from this I have keep paper records of lambing at the time and use these to estimate gestation dates (so far a reasonable degree of intra-animal consistency) and note down any problems.
To begin with, with only a few sheep, record everything - it won't be that much work and a notebook will be sufficient. Over time you'll get a feel for what data helps you most and you can refine things. But my advice would be definitely note down any problems so you can spot any trends and definitely record weights.