Welcome to the forum,
Before I talk about exhausts have you thought about putting in a cone air filter (Revo - £360 ish) which would give you some more noise from the engine on power and letting off.
There are many companies for exhausts but it all comes down to budget...
You can remove the silencer just after the cat with a straight through pipe for about £90 whcih gives a nicer noise but I'm unsure on MOT rules these days.
Then you can get a BCS (Powervalve) resonated cat back exhaust for about £600 which should give you a deeper tone, if you want it louder than that you can get a non resonated exhaust but you may find that your neighbors might not like you much on early morning starts -
https://www.powervalve.co.uk/products/seat/leon.html
Or you could get a downpipe and 200 cell cat fitted which should improve noise slightly again for about £600 I think (normally used for mapping stage 2 I think)
Few brands to look at
Jetex -
https://www.jetex.co.uk/performance-exhausts/
Milltek and Scorpion -
https://progressiveparts.com/parts/exhaust/exhaust-systems
BCS (Powervalve) -
https://www.powervalve.co.uk/products/seat.html
Cobra -
http://cobrasport.com/index.php/cobra-sport-exhaust/seat/leon.html
If you want a nice noise but not too loud you could get in contact with BCS and get a resonated exhaust but they do it modular so you could turn into non res if you so wanted (others may do this also)
Hope this helps
Cheers