Just a thought…while it can be a good idea to give up something (or start a new habit) that will be permanent, there is something to doing something just during Lent. For one thing, there is the idea of penance that some mentioned. Giving up something for Lent is a constant reminder of the season and of what God has done for us.
Or, if you have a bigger goal…for example, maybe you find you have problems with responding in irritation to certain people and need to grow in self control. Supposedly fasting will help with that. So to fast certain days during Lent (not just Ash Wednesday and Good Friday) … or to at least fast from something important to you…might help you get started on the road to self control, without the need to commit permanently.
That is just a “for example”, of course. There are things to do besides fasting from something, depending on what you think would help you grow in holiness.
And having said that…in 2008 I made a commitment for Lent that ended up becoming permanent.

It happens, even without the intent.