Hi, welcome to the game, congratulations on your first Munros.
One of the benefits of going back to the same area (around Killin) is that you can get some more nice high starts to your walks, this will help you ease into the hill-walking effort! Meall nam Tarmachan is a great hill, along with its ridge, and you're at 450m to start (it's opposite and at a similar start height to your jaunt up Ben Lawers). Stuchd an Lochain is another good hill with a 400m start and from the same startpoint there's Meall Buidhe on the other side of Loch an Daimh; in fact if you're feeling really strong both can be done in a day.
There's plenty more around Glens Lyon and Lochay as the guys have said.
Then there's Cruach Ardrain and Beinn Tulaichean as an introduction to the Crianlarich hills, these can be approached from the north or south.
Happy hunting!