
Huxley Training aid is all you need for indoors - I have the 4-metre one and it does everything I need to teach a good putting stroke. You can get various types of Huxley's but the training aid is the best value IMHO - it comes with a foot board, elastic string, hole reducer and some foam pads to alter the breaks.
Add in a putting guide from www.puttingguide.se and you have all you need to work on your stroke for under £500.
Hope this helps.
Parky