Finding a template/oligo combination for my first PCR experiment
You need a genome that isn't too complex, which suggests something microbial. You also need a genome that is well-characterised : either fully- sequenced, or with lots of sequenced genes to allow you to design primers. And finally you need a readily accessible source of material for DNA extraction.

I would suggest either dried yeast, as a source of Saccharomyces cerevisiae DNA, or live yoghurt as a source of DNA from Lactobacilli. You could even try culturing something from yoghurt to get pure bacterial colonies: since these would be from a food source there should be minimal risk.

You might be tempted by one of the traditional plant sources of DNA (e.g. onions) , but it can be tricky to avoid copurifying polysaccharides which inhibit DNA-related enzymes.

Finally, if you do culture some bacteria, or even if you use dried yeast, you probably wouldn't need to actually prepare DNA at all. PCR direct from bacterial cells is widely used - the 95 C step will release sufficient DNA.

added later in response to comment by OP

I chose to follow up on Lactobacillus delbrueckii subsp. bulgaricus because I found this coming up over and over again with reference to yoghurt. If you were to test a range of yoghurts I think you could be fairly confident that this would be present.

There are 5 published genomes for different strains of the species Lactobacillus delbrueckii including subspecies bulgaricus (various strains) and lactis. How different are they? I decided to look at one gene, and lactate dehydrogenase seemed like a logical choice (it produces the lactic acid).

The complete nucleotide sequence for the lactate dehydrogenase gene from Lactobacillus delbrueckii subsp. bulgaricus ATCC 11842 is here. If you run a BLAST from that page limiting the search to Lactobacilli (taxid 1578) you do indeed find hits to the gene from several other genomes. Here is a representative selection from the sequence alignment to the least similar of the hits:

Query  99766   CCTTCCACGCTTCTGGAGGTACTGAATTCGCCCTGGCTCAACTGGGCAACGATGCCGGTA  99825
               ||||||||||||||| ||||||||||||||||||||| ||||||||||||||||||||||
Sbjct  90616   CCTTCCACGCTTCTGAAGGTACTGAATTCGCCCTGGCCCAACTGGGCAACGATGCCGGTA  90675

Query  99826   TGTACGGTGCCGTTAAGATGGTTCTGTAATTTTGAATGTAAAAAAGCACCAGGCTTTTAA  99885
               ||||||||||||||||||||||||||||||||||||| |||||||||||||| |||||||
Sbjct  90676   TGTACGGTGCCGTTAAGATGGTTCTGTAATTTTGAATATAAAAAAGCACCAGACTTTTAA  90735

Query  99886   AGTCTGGTGCtttttttGTTTATCCTAAAGAGTCCAGGGTTGCCTTTATCGTCGCGGCTG  99945
               |||||||||||| |||||||||| |||||||||||||||||||||| |||||||||||||
Sbjct  90736   AGTCTGGTGCTTATTTTGTTTATTCTAAAGAGTCCAGGGTTGCCTTCATCGTCGCGGCTG  90795

Query  99946   AGGCCCGCATCTTGGCCAATTCGCTGTCATTTAACGGCAATTCCAGTACGTGGCTGATCC  100005
               ||||| |||||||||||||||||||||||||||||||||||||||| ||||||||||| |
Sbjct  90796   AGGCCTGCATCTTGGCCAATTCGCTGTCATTTAACGGCAATTCCAGCACGTGGCTGATTC  90855

Query  100006  CTTGTCCGTTGATGATGGCCAGGGTGCCCAGGTAGATCTCATCCTTGATCCCGTATTCCC  100065
               |||| |||||||||||||||||||||||||| ||||||||||||||||||||||||||||
Sbjct  90856   CTTGCCCGTTGATGATGGCCAGGGTGCCCAGATAGATCTCATCCTTGATCCCGTATTCCC  90915

Query  100066  CGTGCAATGGTGCGGAAAGAGGCAGGGCCAGGTCGTTGTTTTCCAAAATGGCCGTCACGA  100125
               |||||||||| ||||||||||||||||||||||||||||||||||||||||||| |||||
Sbjct  90916   CGTGCAATGGCGCGGAAAGAGGCAGGGCCAGGTCGTTGTTTTCCAAAATGGCCGCCACGA  90975

Query  100126  TCTTGGCCAGCATCATGGCCACGCCATAGTAGGTTGCGCCCTTTTTGACGATAATCTCGC  100185
               |||||||||||||||||||||||||||||||||| |||||||||||| |||| |||||||
Sbjct  90976   TCTTGGCCAGCATCATGGCCACGCCATAGTAGGTCGCGCCCTTTTTGCCGATGATCTCGC  91035


As you can see, there are some differences, but there should be no problem designing primers matching both (again - this is just one part of the gene). Obviously you might wish to make an alignment for all 5 sequences, but I got the impression that at least some of the others were identical to the query, even though they are from different subspecies. These are very closely-related organisms.

In terms of your experiment, I suggest that you plan to use a range of yoghurts and/or starters as the source of template. You could even mix them, if there are constraints on your set-up.