You can fit any PC speakers you want provided the jack plug fit's into your laptop's speaker-out jack (usually a 3.5mm audio jack). Your current speakers are probably not "active" ones, which means they are not mains-powered so they have no amplifier, or have only a weak amplifier. Hence insufficient volume.
Look for a pair ("2.1" is better) which have built-in amplifier. A "2.1" speaker set has two small speakers plus a larger, third speaker (hence the name "2.1") called a "woofer" which gives deep bass sound. Even with a 2.1 speaker set, you still only need to plug a single jackplug into your laptop, so don't worry that you haven't got enough connections for 3 speakers.
Any PC speaker set which plugs into the mains will have a built-in amplifier (that's what the mains power is required for).