Google g m tools . They have various no. Travishers at about 40 quidI've got a couple and they work well
I bought a No.3 travisher from G&M which is a nice tool but difficult to use (difficult for me anyway!) I think any steeper than No.3 might be too much. I just made a concaving tool out of an old coffin plane like somone else on the forum did. I've test fired it on pine and it looks like it's worked. Travishers are the right shape but as I understand it they are more for shaving across the grain. Chair makers seems to use them for making those little dents for your bum to nestle into!