Heated propagators

Heated propagators

I have a question. I want to germinate the seed of sub-tropical plants. Last year I had a few that didn't work out for me, so it's time for a heated propagator. However, I don't want to pay out for one with thermostatic control and sellers give no idea of what temperature they are able to maintain and in what ambient temperature. Can I get away with an eight watt model, which seems the cheapest, or am I likely to need something with more wattage to keep the temperature at what's needed, which I guess is about 25C/77F for, say, tender passiflora species? I'm zone 8, have a (crowded) windowsill indoors and a frost-free greenhouse - i'd rather use the latter. Thanks for your help.
The Natives are restless!

The Natives are restless!

you can almost hear the corn grow!

you can almost hear the corn grow!

In my garden this morning

In my garden this morning

Too much stuufff

Too much stuufff

plant id

plant id

I’m new to the community

I’m new to the community