The extensions I use are from Foxy Locks and they are superb! They can last upto 6 months or more depending how you care for them. Mine usually last for around 5 months-ish. That's because I sleep with them in as I'm too lazy to take them out and reapply them again in the morning. They are clip in extensions and they offer a wide range of lengths, colours and thickness. They are seamless clip in which means you people don't see the clips very easily. Below are the ones get and they are 20 inch's long and weigh 165g. I choose the colour Cocoa which is a very dark brown.
I would 100% recommend these extensions to anyone looking to get extensions and are new to extensions. I use extensions for length but you are also able to use them to add thickness as well.