You probably know what birds you can keep, but you may want to try changing or moving on to a different species-try birds to keep 2 if you want a more challenging species to breed.

Zebra Finches.
Colourful, lively birds with lots of mutations. Seed eaters, provide cuttlefish, grit and egg food when breeding.
Coconut fibres and short lengths of wool make perfect nesting materials.
Standard finch boxes are fine for breeding. You can make your own, 5 x 5 x 5 inches  half open fronts ( 5 x 2.5 inches).
Will breed in Cage or an aviary.
Best Pair Option-Normal Cock and Fawn Hen.
Only cocks have cheek patches and chest bars.
(Although Black cheeked hens  have slight cheek patching.)
Bengalese
Similar in upkeep to zebras.  More passive in nature. A species of finch that does not exist in the wild and believed in be hybridised  by ancient Chinese from mountain mannikin finches.
Lots of mutations.
Used to foster chicks from other species including Gouldian's.
Bengalese are mannikins like silverbills and nuns.
Can only be sexed by behaviour-Male does a manic song and bounce dance when in courtship. Fun to watch.

Silverbills
Very lively little birds.
A truly overlooked species.
Impossible to sex (whatever anyone tries to bullsh** you)
So buy  half of dozen and 'ring' females when nest building.
Seedeaters. Use small 'basket' nests.
Best Option-Indian silverbill.
African Silverbill-darker and prone to crossbeak (check state of beaks carefully before you buy).
Chocolate mutations now bred.
Some breeders colour feed ( phew?) 

OTHER FINCHES
Lavenders, gold breasts, cordon bleu's, Blue caps, Fire finches…...there are many BUT
these all require
heating in winter AND live food when Breeding.