Hi Sarah. Im looking for the same. I'm currently using a crossman m4 .177 multipump. This is well within the ft lb requirements for competition shooting if that's what you wanting to shoot. Its generally all plastic so very light. There are other multipump rifles such as crossman pumpmaster p if u like pink guns.
If your after a more tradional looking rifle like me then im leaning towardd smk target qb78 or brocock concept. Smk is co2 and about 150 quid. Brocock is Pcp and around 350quid. Both are around 2.5 to 3kg