Thierry,
Often chronic insomnia is related to other issues. The most common are overstimulation and not drinking enough water. Overstimulation can be due to excess caffeine consumption, or consumption late in the day. Another common one is watching TV or movie close to bedtime. When you are watching a screen, computer or TV, your mind becomes closely involved in the screen to the extent of completely losing track of the body. This can lead to not noticing your natural tiredness, pushing beyond it and ending up exhausted but unable to let go and sleep.
Practising just before bedtime is not necessarily the most effective time to practice, laying down for 5 minutes and trying to observe sensations will achieve very little as it typically takes 10 minutes or so for the human bodymind to enter fully into any activity.
I'd suggest firstly you ensure you are drinking enough water daily, forget caffeinated drinks after midday, turn off all computers and screens at least half an hour before you want to sleep. Sit and notice what your mind is doing ... Is it running round in circles? Ruminating the day or unresolved life events? If so note this then pay attention to how your body feels, how your breathing feels. Breathe in and relax, breathe out and relax, if you find the mind has wandered back to old stories or the iniquities of the day then note it again and return to feeling body and breath, relaxing with each in and out breath.
Do this seated in a chair or on the floor or a cushion, wherever you are comfortable, but not in bed - bed is for sleeping in. Do it for thirty minutes, minimum twenty. Don't do it immediately prior to bedtime. Afterwards you can listen to some gentle music, just sit and relax or slowly tidy up your place (this one works for me).
Not only is bed only for sleeping in but the whole bedroom. If you have a TV in there consider moving it out.
Meditation is limited in it's ability to have positive effects by your lifestyle and morality/ethical conduct in general, these you have not given any information on. Oh, one last thought - another leading cause is lack of physical exercise. Do you exercise?
Kindly,
Matthew