If you fancy making your own buckle and can find a cheap leather belt in a sale, or recycle an old one, here is a system which requires no special leather tools other than a variable hole punch and a sharp knife.
The new strap, will have to be 70-80mm longer than your usual belt, so the first thing is to establish your belt size. This is done by laying a belt you have been wearing alongside the new one and putting the most used hole of the old belt level with the target one in the new belt. Next mark the new belt just short of the prong tip of the old buckle. This gives you the size. Punch a new single hole here being careful to centre it well. About 7-8cm forward of this, cut the leather across. This end will be on show and can have its corners rounded, or be shaped to a point. Hopefully you will have lost all the unsightly bit that has rivets or stitching.
The buckle which you are going to make should be a rectangle about 3mm wider than the new leather, or quite a bit more if oval. The fixing on the back will consist of a stout double notched peg at one end and a bridge of metal for a double thickness of leather at the other. The peg is made from a stubby piece of 4.5 or 5.0mm round wire and the holes in the leather must match it closely. The bridge at the other end is of oval wire, or rectangular strip approximately 5.0mm wide by 2.5mm thick.
To assemble, push the end with the single hole onto the peg and close to the buckle. Pass the rest of the leather under the bridge, around your waist and under the bridge again. Then push the peg into the chosen of the multiple holes. Some of the surplus which ends up hidden can be cut off.
Alternatively you can buy several straps of similar width, but different colours, say from Le Prevo Leather and change them as the mood takes you. Their minimum order is £10, so you would be ordering 3-4 straps.
As you will have made the buckle yourself it is sure to attract attention. Hallmark the silver and it could become an heirloom. When worn out the leather can easily be replaced. Raw edges can be re-coloured with shoe polish.