T5 checkpoint with torch.save

I have wrapped the T5ForConditionalGeneration class as below:

class T5ConditionalGenerationDoubleHead(nn.Module):
    This is T5 model with 2 heads.
    An LM head + a classification head
    def __init__(self, model_version, num_classes=3, device='cpu'):
        super(T5ConditionalGenerationDoubleHead, self).__init__()
        self.num_classes = num_classes
        self.lm_model = T5ForConditionalGeneration.from_pretrained(model_version)
        self.clf_layer = nn.Linear(in_features=self.lm_model.config.d_model,
        self.device = device

    def forward(self, *args, **kwargs):

        emo_label = kwargs['emolabel']
        kwargs.pop('emolabel', None)
        outputs = self.lm_model(**kwargs, output_hidden_states=True,
        lm_loss = outputs['loss']
        lm_logits = outputs['logits']
        dec_hidden_states = outputs['decoder_hidden_states']
        enc_last_hidden = outputs['encoder_last_hidden_state']
        enc_hidden_states = outputs['encoder_hidden_states']
        last_dec_hidden = dec_hidden_states[-1]
        enc_last_hidden_last_timestep = enc_last_hidden[:,-1,:]
        clf_logits = self.clf_layer(enc_last_hidden_last_timestep)
        return lm_loss, lm_logits, clf_logits

I would like to save a checkpoint of this model (save all params both from lm_model and the classification layer). Is there any way to do it once or I have to do it separately?
Using torch.save(model.state_dict(),'./mycheckpoint/model.pth') does not work as this creates a folder containing some data files and a data.pkl (I don’t even know what are those files). I can not also use the save_pretrained function as the model is an nn.Module.

Do you have any ideas?
Thank you in advance.