If you haven't been to Thailand before then Umphang is perfectly located for accessing jungle adventure packages. It's located in the North west of Thailand and is quieter than many of the backpacker places. At Umphang you can purchase tours that include: trekking, rafting, elephant riding, staying in authentic Thai tribal villages, etc.
The packages are well-organised and include accommodation, meals, guides, and transport.
It is cheap, so the accommodation is not plush, but the food is good.
One word of warning, don't go in September or October (the wet season) as it is likely to rain a great deal of the time. I went at the beginning of August and it rained a fair bit then, (not just the the odd hour or two). To be safe, avoid August as well.
The Da Fiore bacaro and restaurant on Calle delle Botteghe, just off Campo Santo Stefano is wonderful - sip an 'ombra' (red wine), 'spritz' (typical Venetian drink, with Aperol or Campari), or treat yourself to a glass or two of prosecco. Nibble some of the cicheti while sitting at the outside bar and get to know the locals who flock over from local businesses - there is always someone who'll want to talk. Make it your local for the duration of your stay!